This research was supported by the Global Frontier Research Program (NRF-2015M3A6A8065833), and the Basic Science&#160;Research Program (2018R1A6A1A03024940)&#160;through the National Research Foundation of Korea (NRF) funded&#160;by the Korea government.&#160;

1. Plasmid Construction
<ol>
	<li>Construct an expression plasmid (pBAD-dual-TPL-GFP-WT) that expresses the TPL gene from Citrobacter freundii under the control of a constitutive promoter and the green fluorescent protein (GFP) gene with a His6-tag under the control of the araBAD promoter. For pBAD-dual-TPL-GFP-E90TAG, replace the codon for the site (E90) of DOPA with an amber codon (TAG), using a site-directed mutagenesis protocol. The details for the construction of this plasmid was described in our previous report18.</li>
	<li>Construct a tRNA/aaRS-expressing plasmid (pEVOL-DHPRS2)18,19 for the genetic incorporation of DOPA. pEVOL is a special plasmid vector expressing two copies of aaRS genes with independent promoters, and the detailed information of the plasmid is described in a previous report19.</li>
	<li>Use commercially available plasmid preparation kits to obtain high purity plasmid DNAs. Check the purity of the prepped DNAs by using agarose gel electrophoresis, if necessary.</li>
</ol>
2. Culture Preparation
<ol>
	<li>Electroporation
	<ol>
		<li>Use the electro-competent E. coli DH10&#946; strain for this experiment. Add 1 &#181;L of each plasmid DNA (pEVOL-DHPRS2 and pBAD-dual-TPL-GFP-E90TAG) to 20 &#181;L of competent cells. Mix them gently to make a homogeneous mixture, using a pipette.</li>
		<li>Transfer the mixture to the electroporation cuvettes. Place the cuvette in the electroporation chamber. Push the cuvette into the chamber to make firm cuvette-chamber contact.</li>
		<li>Shock the cuvette, using 25 &#181;F and 2.5 kV for 0.1-cm cuvettes.</li>
		<li>Add 1 mL of prewarmed super optimal broth (SOC), containing 2% (w/v) tryptone, 0.5% (w/v) yeast extract, 10 mM NaCl, 2.5 mM KCl, 10 mM MgCl2, and 20 mM glucose, to the cuvette, and transfer the cells to a culture tube. Rescue the cells by incubating them for 1 h at 37 &#176;C with shaking.</li>
		<li>Spread 10 - 100 &#181;L of the rescued cells on a lysogeny broth (LB) agar plate containing 35 &#181;g/mL chloramphenicol and 100 &#181;g/mL ampicillin. Incubate the cells at 37 &#176;C for 16 h.</li>
	</ol>
	</li>
	<li>Starter culture preparation
	<ol>
		<li>Inoculate a single transformed colony in 5 mL of LB medium containing antibiotics. Incubate the colony for 12 h at 37 &#176;C with shaking.</li>
	</ol>
	</li>
</ol>
3. Expression and Purification of GFP-E90DOPA by a Biosynthetic System
<ol>
	<li>Expression of GFP-E90DOPA by a biosynthetic system
	<ol>
		<li>Transfer the starter culture (2 mL) to 100 mL of PA-5052 medium20 (50 mM Na2HPO4, 50 mM KH2PO4, 25 mM [NH4]2SO4, 2 mM MgSO4, 0.1% [w/v] trace metals, 0.5% [w/v] glycerol, 0.05% [w/v] glucose, and 5% [w/v] amino acids [pH 7.25]) containing 35 &#181;g/mL chloramphenicol, 100 &#181;g/mL ampicillin, 100 mM pyruvate, 10 mM catechol, 25 mM ammonia, and 300 &#181;M dithiothreitol (DTT) followed by an incubation at 30 &#176;C with shaking.</li>
		<li>Add 2 mL of 0.2% (w/v) L-arabinose when the optical density (OD) at 550 nm reaches 0.8. Incubate the sample for 12 h at 30 &#176;C with shaking.</li>
		<li>Spin down the cells at 11,000 x g for 5 min, discard the supernatant, and freeze the cell pellet at -80 &#176;C.</li>
	</ol>
	</li>
	<li>Cell lysis
	<ol>
		<li>Thaw the cell pellet on ice and resuspend the cells in 10 mL of lysis buffer containing 50 mM NaH2PO4 (pH 8.0), 10 mM imidazole, and 300 mM NaCl.</li>
		<li>Sonicate the resuspended cells on ice for 10 min. Use 80% sonication amplitude with a pulse of 25 s on and 35 s off.</li>
		<li>Spin down the cell lysate at 18,000 x g at 4 &#176;C for 15 min. Transfer the supernatant to a fresh tube for purification and discard the pellet.</li>
	</ol>
	</li>
	<li>Ni-NTA affinity chromatography
	<ol>
		<li>Add Ni-NTA (nitrilotriacetic acid) resin (300 &#181;L of resin suspension for a 100-mL culture) to the supernatant and bind the proteins to the Ni-NTA resin at 4 &#176;C by gently shaking the suspension for 1 h.</li>
		<li>Transfer the suspension to a polypropylene column and wash the resin 3x with 5 mL of wash buffer containing 50 mM NaH2PO4 (pH 8.0), 20 mM imidazole, and 300 mM NaCl.</li>
		<li>Elute the proteins 3x with 300 &#181;L of elution buffer containing 50 mM NaH2PO4 (pH 8.0), 250 mM imidazole, and 300 mM NaCl.</li>
		<li>Determine the protein concentration by measuring the absorbance at 280 nm. The extinction coefficient (24,630 M-1cm-1) for GFP-E90DOPA at 280 nm was calculated by a protein extinction coefficient calculator (e.g., https://web.expasy.org/protparam/) and the independently measured extinction coefficiennt (2630 M-1cm-1) for DOPA. As an alternative method, use the Bradford protein assay21 for a determination of the protein concentration.</li>
	</ol>
	</li>
</ol>
4. Oligomerization of Purified GFP-E90DOPA
<ol>
	<li>Add 1 &#181;L of sodium periodate in H2O (6 mM) (1.0 equiv. to GFP-E90DOPA) to a solution of 20 &#181;L of GFP-E90DOPA (300 &#181;M) in a phosphate buffer containing 50 mM Na2HPO4 (pH 8.0) and 300 mM NaCl.</li>
	<li>Allow the oligomerization reaction to proceed at 25 &#176;C for 48 h.</li>
	<li>Analyze the reaction mixture by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) (SDS-PAGE) as described in step 6.</li>
</ol>
5. Conjugation of GFP-E90DOPA with an Alkyne Probe by SPOCQ
<ol>
	<li>Add 1 &#181;L of the Cy5.5-linked azadibenzocyclooctyne (Cy5.5-ADIBO)22 in H2O (4.0 mM) (10 equiv. to GFP-E90DOPA) to a solution of 20 &#181;L of GFP-E90DOPA (20 &#181;M) in a phosphate buffer containing 50 mM Na2HPO4 (pH 8.0) and 300 mM NaCl.</li>
	<li>Add 1 &#181;L of sodium periodate in H2O (400 &#181;M) (1.0 equiv. to GFP-E90DOPA) to the reaction mixture.</li>
	<li>Allow the SPOCQ reaction to proceed at 25 &#176;C for 1 h. If a light-sensitive probe is used, cover the reaction vessel with aluminum foil.</li>
</ol>
6. Purification of the Labeled GFP
<ol>
	<li>Dilute the SPOCQ reaction mixture by adding a phosphate buffer, containing 50 mM Na2HPO4 (pH 8.0) and 300 mM NaCl, up to 500 &#181;L.</li>
	<li>Transfer the diluted solution to a centrifugal filter spin column. Centrifuge the spin column at 14,000 x g at 4 &#176;C for 15 min and discard the flow-through. Repeat this step 3x in order to remove any excess Cy5.5-ADIBO.</li>
	<li>Transfer the purified sample from the spin column to a 1.5-mL microcentrifuge tube.</li>
	<li>Alternatively, carry out a purification by dialysis against the same buffer.</li>
	<li>Store the purified GFP at 4 &#176;C.</li>
</ol>
7. SDS-PAGE Analysis and Fluorescence Gel Scanning
<ol>
	<li>Prepare protein samples for SDS-PAGE analysis by adding 5 &#181;L of protein sample buffer (see Table of Materials) and 2 &#181;L of DTT (1.00 M) to 13 &#181;L of purified, or crude, labeled GFP (13.6 &#181;M or 0.38 mg/mL). For an analysis of oligomeric GFP, use a higher concentration of GFP (67.8 &#181;M or 1.9 mg/mL). Denature the proteins by incubating them at 95 &#176;C for 10 min.</li>
	<li>Place a 4% - 12% Bis-Tris SDS-PAGE gel cassette (purchased, premade gel cassettes) to the electrophoresis cell and add a running buffer (see Table of Materials). Load the protein samples and a molecular weight marker. Run the electrophoresis for 35 - 40 min at 200 V. 
	NOTE: Avoid any exposure of the protein samples to light by carrying out all processes in the dark, to minimize photo-bleaching of the fluorescent probe.</li>
	<li>Use a fluorescence scanner for fluorescence imaging. Wrap a protein gel from electrophoresis and place it on a fluorescence scanner. Scan the gel by using an appropriate wavelength setting. For Cy5.5, select the Cy5 mode provided in the scanner software.</li>
	<li>Stain the gel with a commercial protein staining reagent.</li>
</ol>
8. MALDI-TOF MS Analysis by Trypsin Digestion
<ol>
	<li>Incubate 100 &#181;L of purified GFP-E90DOPA (2.2 mg/mL or 80 &#181;M) in a buffer containing 50 mM Tris-HCl (pH 8.0), 0.1% (w/v) SDS, and 25 mM DTT at 60 &#176;C for 1 h.</li>
	<li>Add 1 &#181;L of Iodoacetamide in H2O (IAA, 4.0 M) (500 equiv. to GFP-E90DOPA) to the purified GFP-E90DOPA solution (80 &#181;M) in the same buffer. Incubate the mixture at 25 &#176;C for 30 min with protection from light.</li>
	<li>Digest the GFP-E90DOPA sample by adding trypsin (1:100 protease-to-substrate-protein ratio [w/w]) and incubate the reaction mixture at 37 &#176;C for 4 h.</li>
	<li>Purify the digested peptide sample by using a standard desalting method with C18 spin columns.</li>
	<li>Analyze the digested peptides by the reported protocol for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) using alpha-cyano-4-hydroxycinnamic acid (CHCA) as a matrix23.</li>
</ol>

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The authors have nothing to disclose.

In this protocol, the biosynthesis and direct incorporation of DOPA are described. The bacterial cell used in this method can synthesize an additional amino acid and use it as an unnatural building block for protein synthesis. The genetic incorporation of unnatural amino acids has been a key technology for the development of unnatural organism with an expanded genetic code. However, this method has been technically incomplete and is being modified to improve incorporation efficiency and minimize perturbation to endogenou...

DOPA is an amino acid involved in the biosynthesis of catecholamines in animals and plants. This amino acid is synthesized from Tyr by tyrosine hydroxylase and molecular oxygen (O2)1. Because DOPA is a precursor of dopamine and can permeate the blood-brain barrier, it has been used in the treatment of Parkinson&#39;s disease2. DOPA is also found in mussel adhesion proteins (MAPs), which are responsible for the adhesive properties of mussels in wet conditions3,4,5,6,7. Tyr is initially encoded at the positions where DOPA is found in MAPs and is then converted into DOPA by tyrosinases8,9. Because of its interesting biochemical properties, DOPA has been used in a variety of applications. The dihydroxyl group of DOPA is chemically prone to oxidation, and the amino acid is easily converted into L-dopaquinone, a precursor of melanins. Owing to its high electrophilicity, L-dopaquinone and its derivatives have been used for crosslinking and conjugation with thiols and amines10,11,12,13. 1,2-Quinones can also function as a diene for cycloaddition reactions and have been used for bioconjugation by strain-promoted oxidation-controlled cyclooctyne-1,2-quinone (SPOCQ) cycloaddition14. In addition, the dihydroxyl group can chelate metal ions such as Fe3+ and Cu2+, and proteins containing DOPA have been utilized for drug delivery and metal ion sensing15,16.
DOPA has been genetically incorporated into proteins by using an orthogonal aminoacyl-tRNA (aa-tRNA) and aminoacyl-tRNA synthetase (aaRS) pair17 and used for protein conjugation and crosslinking10,11,12,13. In this report, experimental results and protocols for the genetic incorporation of DOPA biosynthesized from cheap starting materials and its applications to bioconjugation are described. DOPA is biosynthesized using a TPL and starting from catechol, pyruvate, and ammonia in Escherichia coli. The biosynthesized DOPA is directly incorporated into proteins by expressing an evolved aa-tRNA and aaRS pair for DOPA. In addition, the biosynthesized protein containing DOPA is site-specifically conjugated with a fluorescent probe and crosslinked to produce protein oligomers. This protocol will be useful for protein scientists, to biosynthesize mutant proteins containing DOPA and conjugate the proteins with biochemical probes or drugs for industrial and pharmaceutical applications.

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		<tr height="21">
			<td height="21" style="height:21px;width:596px;">1. Plasmid Construction</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">Plasmid pBAD-dual-TPL-GFP-E90TAG</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td>optionally contain the amber stop codon(TAG) at a desired position. Ko, W. et al. Efficient and Site-Specific Antibody Labeling by Strain-promoted Azide-Alkyne Cycloaddition. BKCS. 36 (9), 2352-2354, doi: 10.1002/bkcs.10423, (2015)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Plasmid pEvol-DHPRS2</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td>1. Young, T. S., Ahmad, I., Yin, J. A., and Schultz, P. G. An enhanced system for unnatural amino acid mutagenesis in E. coli. J. Mol. Biol. 395 (2), 361-374, doi: 10.1016/j.jmb.2009.10.030, (2010) 2. Kim, S., Sung, B. H., Kim, S. C., Lee, H. S. Genetic incorporation of l-dihydroxyphenylalanine (DOPA) biosynthesized by a tyrosine phenol-lyase. Chem. Commun. 54 (24), 3002-3005, doi: 10.1039/c8cc00281a (2018).</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">DH10&#946;</td>
			<td style="width:167px;">Invitrogen</td>
			<td style="width:133px;">C6400-03</td>
			<td>Expression Host</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Plasmid Mini-prep kit</td>
			<td style="width:167px;">Nucleogen</td>
			<td style="width:133px;">5112</td>
			<td>200/pack</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Agarose</td>
			<td style="width:167px;">Intron biotechnology</td>
			<td style="width:133px;">32034</td>
			<td>500 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Ethidium bromide</td>
			<td style="width:167px;">Alfa Aesar</td>
			<td style="width:133px;">L07482</td>
			<td>1 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">LB Broth</td>
			<td style="width:167px;">BD Difco</td>
			<td style="width:133px;">244620</td>
			<td>500 g</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:596px;">2. Culture preparation</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:596px;">2.1) Electroporation</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Micro pulser&#160;</td>
			<td style="width:167px;">BIO-RAD</td>
			<td style="width:133px;">165-2100</td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Micro pulser cuvette</td>
			<td style="width:167px;">BIO-RAD</td>
			<td style="width:133px;">165-2089</td>
			<td style="width:339px;">0.1 cm electrode gap, pkg. of 50</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Ampicillin Sodium</td>
			<td style="width:167px;">Wako</td>
			<td style="width:133px;">018-10372</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Chloramphenicol</td>
			<td style="width:167px;">Alfa Aesar</td>
			<td style="width:133px;">B20841</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Agar</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">214230</td>
			<td>500 g</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">SOC medium</td>
			<td style="width:167px;">Sigma</td>
			<td style="width:133px;">S1797</td>
			<td>100 mL</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">3. Expression and Purification of GFP-E90DOPA by biosynthetic system</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:21px;width:596px;">3.1 Expression of GFP-E90DOPA by biosynthetic system</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L(+)-Arabinose, 99%</td>
			<td style="width:167px;">Acros</td>
			<td style="width:133px;">104981000</td>
			<td>100 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Pyrocatechol, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">P1387</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Ammonium sulfate, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">A0943</td>
			<td>500 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">pyruvic acid, 98%</td>
			<td style="width:167px;">Alfa Aesar</td>
			<td style="width:133px;">A13875</td>
			<td>100 g</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:21px;width:596px;">Sodium phosphate dibasic, anhydrous, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">S0891</td>
			<td>1 kg</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Potassium phophate, monobasic, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">P1127</td>
			<td>1 kg</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Magnesium sulfate, anhydrous, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">M0146</td>
			<td>1 kg</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">D(+)-Glucose, anhydrous, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">D0092</td>
			<td>500 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Glycerol, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">G0269</td>
			<td>1 kg</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Trace metal mix a5 with co</td>
			<td style="width:167px;">Sigma</td>
			<td style="width:133px;">92949</td>
			<td>25 mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Proline, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">P1257</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Phenylalanine, 98.5%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">P1982</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Tryptophane</td>
			<td style="width:167px;">JUNSEI</td>
			<td style="width:133px;">49550-0310</td>
			<td>25 g</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">L-Arginine, 98%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">A1149</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Glutamine, 98%</td>
			<td style="width:167px;">JUNSEI</td>
			<td style="width:133px;">27340-0310</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Asparagine monohydrate, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">A1198</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Methionine</td>
			<td style="width:167px;">JUNSEI</td>
			<td style="width:133px;">73190-0410</td>
			<td>25 g</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">L-Histidine hydrochloride monohydrate, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">H0604</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Threonine, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">T2938</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Leucine</td>
			<td style="width:167px;">JUNSEI</td>
			<td style="width:133px;">87070-0310</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Glycine, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">G0286</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Glutamic acid, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">G0233</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Alanine, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">A1543</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Isoleucine, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">I1049</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Valine, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">V0088</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Serine</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">S2447</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Aspartic acid</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">A1205</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">L-Lysine monohydrochloride, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">L0592</td>
			<td>25 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">3.2 Cell lysis</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Imidazole, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">I0578</td>
			<td>1kg</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Sodium phosphate monobasic, 98%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">S0919</td>
			<td>1 kg</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Sodium Chloride, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">S2907</td>
			<td>1 kg</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">Ultrasonic Processor - 150 microliters to 150 milliliters</td>
			<td style="width:167px;">SONIC &#38; MATERIALS</td>
			<td style="width:133px;">VCX130</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">3.3 Ni-NTA Affinity Chromatography</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Ni-NTA resin</td>
			<td style="width:167px;">QIAGEN</td>
			<td style="width:133px;">30210</td>
			<td>25 mL</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">Polypropylene column</td>
			<td style="width:167px;">QIAGEN</td>
			<td style="width:133px;">34924</td>
			<td>50/pack, 1 mL capacity</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:21px;width:596px;">4. Oligomerization of Purified GFP-E90DOPA&#160;</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">Sodium periodate, 99.8&#38;</td>
			<td style="width:167px;">Acros</td>
			<td style="width:133px;">419610050</td>
			<td>5 g</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:21px;width:596px;">5. Conjugation of GFP-E90DOPA with an Alkyne Probe by Strain-Promoted Oxidation-Controlled Cyclooctyne&#8211;1,2-Quinone Cycloaddition (SPOCQ)&#160;</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">Cy5.5-ADIBO&#160;</td>
			<td style="width:167px;">FutureChem</td>
			<td style="width:133px;">FC-6119</td>
			<td>1mg</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">6. Purification of Labeled GFP</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">Amicon Ultra 0.5 mL Centrifugal Filters</td>
			<td style="width:167px;">MILLIPORE</td>
			<td style="width:133px;">UFC500396</td>
			<td>96/pack, 500ul capacity</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">7. SDS-PAGE Analysis and Fluorescence Gel Scanning</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">1,4-Dithio-DL-threitol, DTT, 99.5 %</td>
			<td style="width:167px;">Sigma</td>
			<td style="width:133px;">10708984001</td>
			<td>10 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">NuPAGE LDS Sample Buffer, 4X</td>
			<td style="width:167px;">Thermofisher</td>
			<td style="width:133px;">NP0007</td>
			<td>10 mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">MES running buffer</td>
			<td style="width:167px;">Thermofisher</td>
			<td style="width:133px;">NP0002</td>
			<td>500 mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Nupage Novex 4-12% SDS PAGE gels</td>
			<td style="width:167px;">Thermofisher</td>
			<td style="width:133px;">NO0321</td>
			<td>12 well</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Coomassie Brilliant Blue R-250</td>
			<td style="width:167px;">Wako</td>
			<td style="width:133px;">031-17922</td>
			<td>25 g</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">G:BOX Chemi Fluorescent &#38; Chemiluminescent Imaging System</td>
			<td style="width:167px;">Syngene</td>
			<td style="width:133px;"></td>
			<td>G BOX Chemi XT4</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:21px;width:596px;">8. MALDI-TOF MS analysis by Trypsin Digestion</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:21px;width:596px;">8.1 Preparation of the digested peptide sample by trypsin digestion</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Tris(hydroxymethyl)aminomethane, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">T1351</td>
			<td>500 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Hydrochloric acid, 35~37%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">H0256</td>
			<td>500 mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Dodecyl sulfate sodium salt, 85%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">D1070</td>
			<td>250 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Iodoacetamide</td>
			<td style="width:167px;">Sigma</td>
			<td style="width:133px;">I6125</td>
			<td>5 g</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:596px;">Trypsin Protease, MS Grade</td>
			<td style="width:167px;">Thermofisher</td>
			<td style="width:133px;">90057</td>
			<td>5 x 20 &#181;g/pack</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">C-18 spin columns</td>
			<td style="width:167px;">Thermofisher</td>
			<td style="width:133px;">89870</td>
			<td>25/pack, 200 &#181;L capacity</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:21px;width:596px;">8.2 Analysis of the digested peptide by MALDI-TOF</td>
			<td style="width:167px;"></td>
			<td style="width:133px;"></td>
			<td style="width:339px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Acetonitirile, 99.5%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">A0125</td>
			<td>500 mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">&#945;-Cyano-4-hydroxycinnamic acid</td>
			<td style="width:167px;">Sigma</td>
			<td style="width:133px;">C2020</td>
			<td>10 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Trifluoroacetic acid, 99%</td>
			<td style="width:167px;">SAMCHUN</td>
			<td style="width:133px;">T1666</td>
			<td>100 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">MTP 384 target plate ground steel BC targets</td>
			<td style="width:167px;">Bruker</td>
			<td style="width:133px;">8280784</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:596px;">Bruker Autoflex Speed MALDI-TOF mass spectrometer</td>
			<td style="width:167px;">Bruker</td>
			<td style="width:133px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

genetic incorporation of biosynthesized l-dihydroxyphenylalanine (dopa) and its application to protein conjugation

L-dihydroxyphenylalanine (DOPA) is an amino acid found in the biosynthesis of catecholamines in animals and plants. Because of its particular biochemical properties, the amino acid has multiple uses in biochemical applications. This report describes a protocol for the genetic incorporation of biosynthesized DOPA and its application to protein conjugation. DOPA is biosynthesized by a tyrosine phenol-lyase (TPL) from catechol, pyruvate, and ammonia, and the amino acid is directly incorporated into proteins by the genetic incorporation method using an evolved aminoacyl-tRNA and aminoacyl-tRNA synthetase pair. This direct incorporation system efficiently incorporates DOPA with little incorporation of other natural amino acids and with better protein yield than the previous genetic incorporation system for DOPA. Protein conjugation with DOPA-containing proteins is efficient and site-specific and shows its usefulness for various applications. This protocol provides protein scientists with detailed procedures for the efficient biosynthesis of mutant proteins containing DOPA at desired sites and their conjugation for industrial and pharmaceutical applications.

The expression system for the direct incorporation of DOPA biosynthesized from a TPL is shown in Figure 1. The genes for the evolved aa-tRNA and aaRS pair are placed in a plasmid, and the GFP gene (GFP-E90TAG) containing an amber codon at position 90 is located in another plasmid to evaluate the incorporation of DOPA by GFP fluorescence. The TPL gene is placed in the same expression plasmid containing the GFP gene and constitutively expressed to maximize the ...

Watch this Scientific Journal Video about Genetic Incorporation of Biosynthesized L-dihydroxyphenylalanine DOPA and Its Application to Protein Conjugation at JoVE.com

Genetic Incorporation of Biosynthesized L-dihydroxyphenylalanine DOPA and Its Application to Protein Conjugation

Here, we present a protocol for the genetic incorporation of L-dihydroxyphenylalanine biosynthesized from simple starting materials and its application to protein conjugation.

Genetic Incorporation of Biosynthesized L-dihydroxyphenylalanine (DOPA) and Its Application to Protein Conjugation

L-dihydroxyphenylalanine (DOPA) is an amino acid found in the biosynthesis of catecholamines in animals and plants. Because of its particular biochemical ...

genetic-incorporation-biosynthesized-l-dihydroxyphenylalanine-dopa

Research

JoVE Journal

Biochemistry

7.8K Views.  Sogang University. Here, we present a protocol for the genetic incorporation of L-dihydroxyphenylalanine biosynthesized from simple starting materials and its application to protein conjugation.

Video: Genetic Incorporation of Biosynthesized L-dihydroxyphenylalanine DOPA and Its Application to Protein Conjugation

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating these studies, reincorporation of detergent-solubilized membrane proteins into liposomes is a stochastic process where protein topology is impossible to enforce. This paper offers an alternative method to these challenging techniques that utilizes a liposome-based scaffold. Protein solubility is enhanced by deletion of the transmembrane domain, and these amino acids are replaced with a tethering moiety, such as a His-tag. This tether interacts with an anchoring group (Ni2+ coordinated by nitrilotriacetic acid (NTA(Ni2+)) for His-tagged proteins), which enforces a uniform protein topology at the surface of the liposome. An example is presented wherein the interaction between Dynamin-related protein 1 (Drp1) with an integral membrane protein, Mitochondrial Fission Factor (Mff), was investigated using this scaffold liposome method. In this work, we have demonstrated the ability of Mff to efficiently recruit soluble Drp1 to the surface of liposomes, which stimulated its GTPase activity. Moreover, Drp1 was able to tubulate the Mff-decorated lipid template in the presence of specific lipids. This example demonstrates the effectiveness of scaffold liposomes using structural and functional assays and highlights the role of Mff in regulating Drp1 activity.

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

This paper describes a method for assessing the interactions and assemblies of integral membrane proteins in vitro with various partner factors in a lipid-proximal environment.

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating ...

A Protein Preparation Method for the High-throughput Identification of Proteins Interacting with a Nuclear Cofactor Using LC-MS/MS Analysis

Transcriptional coregulators are vital to the efficient transcriptional regulation of nuclear chromatin structure. Coregulators play a variety of roles in regulating transcription. These include the direct interaction with transcription factors, the covalent modification of histones and other proteins, and the occasional chromatin conformation alteration. Accordingly, establishing relatively quick methods for identifying proteins that interact within this network is crucial to enhancing our understanding of the underlying regulatory mechanisms. LC-MS/MS-mediated protein binding partner identification is a validated technique used to analyze protein-protein interactions. By immunoprecipitating a previously-identified member of a protein complex with an antibody (occasionally with an antibody for a tagged protein), it is possible to identify its unknown protein interactions via mass spectrometry analysis. Here, we present a method of protein preparation for the LC-MS/MS-mediated high-throughput identification of protein interactions involving nuclear cofactors and their binding partners. This method allows for a better understanding of the transcriptional regulatory mechanisms of the targeted nuclear factors.

We have established a method for the purification of coregulatory interaction proteins using the LC-MS/MS system.

Transcriptional coregulators are vital to the efficient transcriptional regulation of nuclear chromatin structure. Coregulators play a variety of roles in ...

Preparation of Keratin Hydrolysate from Chicken Feathers and Its Application in Cosmetics

Keratin hydrolysates (KHs) are established standard components in hair cosmetics. Understanding the moisturizing effects of KH is advantageous for skin-care cosmetics. The goals of the protocol are: (1) to process chicken feathers into KH by alkaline-enzymatic hydrolysis and purify it by dialysis, and (2) to test if adding KH into an ointment base (OB) increases hydration of the skin and improves skin barrier function by diminishing transepidermal water loss (TEWL). During alkaline-enzymatic hydrolysis feathers are first incubated at a higher temperature in an alkaline environment and then, under mild conditions, hydrolyzed with proteolytic enzyme. The solution of KH is dialyzed, vacuum dried, and milled to a fine powder. Cosmetic formulations comprising from oil in water emulsion (O/W) containing 2, 4, and 6 weight% of KH (based on the weight of the OB) are prepared. Testing the moisturizing properties of KH is carried out on 10 men and 10 women at time intervals of 1, 2, 3, 4, 24, and 48 h. Tested formulations are spread at degreased volar forearm sites. The skin hydration of stratum corneum (SC) is assessed by measuring capacitance of the skin, which is one of the most world-wide used and simple methods. TEWL is based on measuring the quantity of water transported per a defined area and period of time from the skin. Both methods are fully non-invasive. KH makes for an excellent occlusive; depending on the addition of KH into OB, it brings about a 30% reduction in TEWL after application. KH also functions as a humectant, as it binds water from the lower layers of the epidermis to the SC; at the optimum KH addition in the OB, up to 19% rise in hydration in men and 22% rise in women occurs.

The goal of the protocol is to prepare keratin hydrolysate from chicken feathers by alkaline-enzymatic hydrolysis and to test whether adding keratin hydrolysate into a cosmetics ointment base improves skin barrier function (heightening hydration and diminishing transepidermal water loss). Tests are conducted on men and woman volunteers.

Keratin hydrolysates (KHs) are established standard components in hair cosmetics. Understanding the moisturizing effects of KH is advantageous for ...

Biotinylated Cell-penetrating Peptides to Study Intracellular Protein-protein Interactions

Here we present a protocol to study intracellular protein-protein interactions that is based on the widely used biotin-avidin pull-down system. The modification presented includes the combination of this technique with cell-penetrating sequences. We propose to design cell-penetrating baits that can be incubated with living cells instead of cell lysates and therefore the interactions found will reflect those that occur within the intracellular context. Connexin43 (Cx43), a protein that forms gap junction channels and hemichannels is down-regulated in high-grade gliomas. The Cx43 region comprising amino acids 266-283 is responsible for the inhibition of the oncogenic activity of c-Src in glioma cells. Here we use TAT as the cell-penetrating sequence, biotin as the pull-down tag and the region of Cx43 comprised between amino acids 266-283 as the target to find intracellular interactions in the hard-to-transfect human glioma stem cells. One of the limitations of the proposed method is that the molecule used as bait could fail to fold properly and, consequently, the interactions found could not be associated with the effect. However, this method can be especially interesting for the interactions involved in signal transduction pathways because they are usually carried out by intrinsically disordered regions and, therefore, they do not require an ordered folding. In addition, one of the advantages of the proposed method is that the relevance of each residue on the interaction can be easily studied. This is a modular system; therefore, other cell-penetrating sequences, other tags, and other intracellular targets can be employed. Finally, the scope of this protocol is far beyond protein-protein interaction because this system can be applied to other bioactive cargoes such as RNA sequences, nanoparticles, viruses or any molecule that can be transduced with cell-penetrating sequences and fused to pull-down tags to study their intracellular mechanism of action.

This is a protocol to study intracellular protein-protein interactions based on the biotin-avidin pull-down system with the novelty of combining cell-penetrating sequences. The main advantage is that the target sequence is incubated with living cells instead of cell lysates and therefore the interactions will occur within the cellular context.

Here we present a protocol to study intracellular protein-protein interactions that is based on the widely used biotin-avidin pull-down system. The ...

High Sensitivity Measurement of Transcription Factor-DNA Binding Affinities by Competitive Titration Using Fluorescence Microscopy

Accurate quantification of transcription factor (TF)-DNA interactions is essential for understanding the regulation of gene expression. Since existing approaches suffer from significant limitations, we have developed a new method for determining TF-DNA binding affinities with high sensitivity on a large scale. The assay relies on the established fluorescence anisotropy (FA) principle but introduces important technical improvements. First, we measure a full FA competitive titration curve in a single well by incorporating TF and a fluorescently labeled reference DNA in a porous agarose gel matrix. Unlabeled DNA oligomer is loaded on the top as a competitor and, through diffusion, forms a spatio-temporal gradient. The resulting FA gradient is then read out using a customized epifluorescence microscope setup. This improved setup greatly increases the sensitivity of FA signal detection, allowing both weak and strong binding to be reliably quantified, even for molecules of similar molecular weights. In this fashion, we can measure one titration curve per well of a multi-well plate, and through a fitting procedure, we can extract both the absolute dissociation constant (KD) and active protein concentration. By testing all single-point mutation variants of a given consensus binding sequence, we can survey the entire binding specificity landscape of a TF, typically on a single plate. The resulting position weight matrices (PWMs) outperform those derived from other methods in predicting in vivo TF occupancy. Here, we present a detailed guide for implementing HiP-FA on a conventional automated fluorescent microscope and the data analysis pipeline.

Here we present a novel method for determining binding affinities at equilibrium and in solution with high sensitivity on a large scale. This improves the quantitative analysis of transcription factor-DNA binding. The method is based on automated fluorescence anisotropy measurements in a controlled delivery system.

Accurate quantification of transcription factor (TF)-DNA interactions is essential for understanding the regulation of gene expression. Since existing ...

Analysis of Protein Folding, Transport, and Degradation in Living Cells by Radioactive Pulse Chase

Radioactive pulse-chase labeling is a powerful tool for studying the conformational maturation, the transport to their functional cellular location, and the degradation of target proteins in live cells. By using short (pulse) radiolabeling times (&lt;30 min) and tightly controlled chase times, it is possible to label only a small fraction of the total protein pool and follow its folding. When combined with nonreducing/reducing SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoprecipitation with (conformation-specific) antibodies, folding processes can be examined in great detail. This system has been used to analyze the folding of proteins with a huge variation in properties such as soluble proteins, single and multi-pass transmembrane proteins, heavily N- and O-glycosylated proteins, and proteins with and without extensive disulfide bonding. Pulse-chase methods are the basis of kinetic studies into a range of additional features, including co- and posttranslational modifications, oligomerization, and polymerization, essentially allowing the analysis of a protein from birth to death. Pulse-chase studies on protein folding are complementary with other biochemical and biophysical methods for studying proteins in vitro by providing increased temporal resolution and physiological information. The methods as described within this paper are adapted easily to study the folding of almost any protein that can be expressed in mammalian or insect-cell systems.

Here we describe a protocol for a general pulse-chase method that allows the kinetic analysis of folding, transport, and degradation of proteins to be followed in live cells.

Radioactive pulse-chase labeling is a powerful tool for studying the conformational maturation, the transport to their functional cellular location, and ...

Application of Biolayer Interferometry (BLI) for Studying Protein-Protein Interactions in Transcription

A transcription factor&#160;(TF) is a protein that regulates gene expression by interacting with the RNA polymerase, another TF, and/or template DNA. GrgA is a novel transcription activator found specifically in the obligate intracellular bacterial pathogen Chlamydia. Protein pulldown assays using affinity beads have revealed that GrgA binds two &#963; factors, namely &#963;66 and &#963;28, which recognize different sets of promoters for genes whose products are differentially required at developmental stages. We have used BLI to confirm and further characterize the interactions. BLI demonstrates several advantages over pulldown: 1) It reveals real-time association and dissociation between binding partners, 2) It generates quantitative kinetic parameters, and 3) It can detect bindings that pulldown assays often fail to detect. These characteristics have enabled us to deduce the physiological roles of GrgA in gene expression regulation in Chlamydia, and possible detailed interaction mechanisms. We envision that this relatively affordable technology can be extremely useful for studying transcription and other biological processes.

Application of Biolayer Interferometry BLI for Studying Protein-Protein Interactions in Transcription

Interactions of transcription factors (TFs) with the RNA polymerase are usually studied using pulldown assays. We apply a Biolayer Interferometry (BLI) technology to characterize the interaction of GrgA with the chlamydial RNA polymerase. Compared to pulldown assays, BLI detects real-time association and dissociation, offers higher sensitivity, and is highly quantitative.

A transcription factor&#160;(TF) is a protein that regulates gene expression by interacting with the RNA polymerase, another TF, and/or template DNA. GrgA ...

PeptiQuick, a One-Step Incorporation of Membrane Proteins into Biotinylated Peptidiscs for Streamlined Protein Binding Assays

Membrane proteins, including transporters, channels, and receptors, constitute nearly one-fourth of the cellular proteome and over half of current drug targets. Yet, a major barrier to their characterization and exploitation in academic or industrial settings is that most biochemical, biophysical, and drug screening strategies require these proteins to be in a water-soluble state. Our laboratory recently developed the peptidisc, a membrane mimetic offering a &#8220;one-size-fits-all&#8221; approach to the problem of membrane protein solubility. We present here a streamlined protocol that combines protein purification and peptidisc reconstitution in a single chromatographic step. This workflow, termed PeptiQuick, allows for bypassing dialysis and incubation with polystyrene beads, thereby greatly reducing exposure to detergent, protein denaturation, and sample loss. When PeptiQuick is performed with biotinylated scaffolds, the preparation can be directly attached to streptavidin-coated surfaces. There is no need to biotinylate or modify the membrane protein target. PeptiQuick is showcased here with the membrane receptor FhuA and antimicrobial ligand colicin M, using biolayer interferometry to determine the precise kinetics of their interaction. It is concluded that PeptiQuick is a convenient way to prepare and analyze membrane protein-ligand interactions within one&#160;day in a detergent-free environment.

We present a method that combines membrane protein purification and reconstitution into peptidiscs in a single chromatographic step. Biotinylated scaffolds are used for direct surface attachment and measurement of protein-ligand interactions via biolayer interferometry.

Membrane proteins, including transporters, channels, and receptors, constitute nearly one-fourth of the cellular proteome and over half of current drug ...

Creating Highly Specific Chemically Induced Protein Dimerization Systems by Stepwise Phage Selection of a Combinatorial Single-Domain Antibody Library

Protein dimerization events that occur only in the presence of a small-molecule ligand enable the development of small-molecule biosensors for the dissection and manipulation of biological pathways. Currently, only a limited number of chemically induced dimerization (CID) systems exist and engineering new ones with desired sensitivity and selectivity for specific small-molecule ligands remains a challenge in the field of protein engineering. We here describe a high throughput screening method, combinatorial binders-enabled selection of CID (COMBINES-CID), for the de novo engineering of CID systems applicable to a large variety of ligands. This method uses the two-step selection of a phage-displayed combinatorial nanobody library to obtain 1) &#34;anchor binders&#34; that first bind to a ligand of interest and then 2) &#34;dimerization binders&#34; that only bind to anchor binder-ligand complexes. To select anchor binders, a combinatorial library of over 109 complementarity-determining region (CDR)-randomized nanobodies is screened with a biotinylated ligand and hits are validated with the unlabeled ligand by bio-layer interferometry (BLI). To obtain dimerization binders, the nanobody library is screened with anchor binder-ligand complexes as targets for positive screening and the unbound anchor binders for negative screening. COMBINES-CID is broadly applicable to select CID binders with other immunoglobulin, non-immunoglobulin, or computationally designed scaffolds to create biosensors for in vitro and in vivo detection of drugs, metabolites, signaling molecules, etc.

Creating chemically induced protein dimerization systems with desired affinity and specificity for any given small molecule ligand would have many biological sensing and actuation applications. Here, we describe an efficient, generalizable method for de novo engineering of chemically induced dimerization systems via the stepwise selection of a phage-displayed combinatorial single-domain antibody library.

Protein dimerization events that occur only in the presence of a small-molecule ligand enable the development of small-molecule biosensors for the ...

JUMPn: A Streamlined Application for Protein Co-Expression Clustering and Network Analysis in Proteomics

With recent advances in mass spectrometry-based proteomics technologies, deep profiling of hundreds of proteomes has become increasingly feasible. However, deriving biological insights from such valuable datasets is challenging. Here we introduce a systems biology-based software JUMPn, and its associated protocol to organize the proteome into protein co-expression clusters across samples and protein-protein interaction (PPI) networks connected by modules (e.g., protein complexes). Using the R/Shiny platform, the JUMPn software streamlines the analysis of co-expression clustering, pathway enrichment, and PPI module detection, with integrated data visualization and a user-friendly interface. The main steps of the protocol include installation of the JUMPn software, the definition of differentially expressed proteins or the (dys)regulated proteome, determination of meaningful co-expression clusters and PPI modules, and result visualization. While the protocol is demonstrated using an isobaric labeling-based proteome profile, JUMPn is generally applicable to a wide range of quantitative datasets (e.g., label-free proteomics). The JUMPn software and protocol thus provide a powerful tool to facilitate biological interpretation in quantitative proteomics.

We present a systems biology tool JUMPn to perform and visualize network analysis for quantitative proteomics data, with a detailed protocol including data pre-processing, co-expression clustering, pathway enrichment, and protein-protein interaction network analysis.