This work was funded by National Institutes of Health grant GM086822 and National Science Foundation major research instrumentation grant DBI-0960313. The authors would like to thank Drs. Jon Miyake &amp; Donna Hardy (Bio-Rad) and Jennifer Loertscher (Seattle University) for their technical expertise. Select chromatography reagents and supplemental instrumentation were generously provided by Bio-Rad.

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	<li>Cummins, P. M., O'Connor, B. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrophobic+interaction+chromatography.">Hydrophobic interaction chromatography.</a> Methods Mol. Biol. 681, 431-437 (2011).</li><li>Nagrath, D., Xia, F., Cramer, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+and+modeling+of+nonlinear+hydrophobic+interaction+chromatographic+systems.">Characterization and modeling of nonlinear hydrophobic interaction chromatographic systems.</a> J. Chromatogr. A. 1218, 1219-1226 (2011).</li><li>To, B. C., Lenhoff, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrophobic+interaction+chromatography+of+proteins.+IV.+Protein+adsorption+capacity+and+transport+in+preparative+mode.">Hydrophobic interaction chromatography of proteins. IV. Protein adsorption capacity and transport in preparative mode.</a> J. Chromatogr. A. 1218, 427-440 (2011).</li><li>Huddleston, J. G., Wang, R., Lyddiatt, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+use+of+mild+hydrophobic+interaction+chromatography+for+"method+scouting"+protein+purification+strategies+in+aqueous+two-phase+systems:+a+study+using+model+proteins.">On the use of mild hydrophobic interaction chromatography for "method scouting" protein purification strategies in aqueous two-phase systems: a study using model proteins.</a> Biotechnol Bioeng. 44, 626-635 (1994).</li><li>Arun, K. H., Kaul, C. L., Ramarao, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Green+fluorescent+proteins+in+receptor+research:+an+emerging+tool+for+drug+discovery.">Green fluorescent proteins in receptor research: an emerging tool for drug discovery.</a> J. Pharmacol. Toxicol. Methods. 51, 1-23 (2005).</li><li>Terrizzi, S. C., Banh, C., Brossay, . <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=L.A+Protocol+for+the+Production+of+KLRG1+Tetramer.">L.A Protocol for the Production of KLRG1 Tetramer.</a> J. Vis. Exp. (35), e1701-e1701 (2010).</li><li>Murphy, P. J. M., Morishima, Y., Kovacs, J. J., Yao, T. P., Pratt, W. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+the+dynamics+of+hsp90+action+on+the+glucocorticoid+receptor+by+acetylation/deacetylation+of+the+chaperone.">Regulation of the dynamics of hsp90 action on the glucocorticoid receptor by acetylation/deacetylation of the chaperone.</a> J. Biol. Chem. 280, 33792-33799 (2005).</li><li>Zeytuni, N., Zarivach, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+of+the+M.+magneticum+strain+AMB-1+Magnetosome+Associated+Protein+MamA&#916;41.">Purification of the M. magneticum strain AMB-1 Magnetosome Associated Protein MamA&#916;41.</a> J. Vis. Exp. (37), 10-3791 (2010).</li><li>Kong, Y., Li, X., Bai, G., Ma, G., Su, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+automatic+system+for+multidimensional+integrated+protein+chromatography.">An automatic system for multidimensional integrated protein chromatography.</a> J. Chromatogr. A. 1217, 6898-6904 (2010).</li><li>Camper, D. V., Viola, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fully+automated+protein+purification.">Fully automated protein purification.</a> Anal. Biochem. 393, 176-181 (2009).</li><li>Hammon, J., Palanivelu, D. V., Chen, J., Patel, C., Minor, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+green+fluorescent+protein+screen+for+identification+of+well-expressed+membrane+proteins+from+a+cohort+of+extremophilic+organisms.">A green fluorescent protein screen for identification of well-expressed membrane proteins from a cohort of extremophilic organisms.</a> Protein Sci. 18, 121-133 (2009).</li><li>Wu, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+green+and+red+fluorescent+proteins+to+teach+protein+expression,+purification,+and+crystallization.">Using green and red fluorescent proteins to teach protein expression, purification, and crystallization.</a> Biochem. Mol. Biol. Educ. 36, 43-54 (2008).</li><li>Queiroz, J. A., Tomaz, C. T., Cabral, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrophobic+interaction+chromatography+of+proteins.">Hydrophobic interaction chromatography of proteins.</a> J. Biotechnol. 87, 143-159 (2001).</li><li>McCue, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theory+and+use+of+hydrophobic+interaction+chromatography+in+protein+purification+applications.">Theory and use of hydrophobic interaction chromatography in protein purification applications.</a> Methods Enzymol. 463, 405-414 (2009).</li></ol>

Select chromatography reagents and supplemental instrumentation were provided by Bio-Rad.

Liquid chromatography techniques have proven invaluable for preparing highly purified proteins necessary for conducting immunological 6, biochemical 7, and structural 8 studies. HIC purification methods most often require empirical determination of a preferred medium, and ligand structure, ligand density, and matrix bead properties all have been shown to impact chromatographic results 2, 3. Automated column scouting is an efficient approach for selecting a HIC medium for subsequent optimization and protein purification 4. The automated column scouting method presented can be readily adapted to various HIC protein purification strategies. Alterations in salt concentration, choice of salt, salt gradient, and pH may further improve purification conditions, and the effects of varying these essential parameters have been previously reviewed 13,14. HIC eluate containing a partially purified target protein can be further purified using a complementary chromatographic technique, such as ion exchange chromatography (IEX) or gel filtration/size exclusion chromatography 9,10.
Because of its unique light absorbance and emission characteristics, the elution profile of GFP can be identified using in-line and post-run approaches. To that end, this protocol can further be adapted for purification of recombinant GFP-fusion proteins, in which an unrelated target protein is &#x201C;tagged&#x201D; with GFP. GFP-tagged target proteins can be detected with UV light 11 and purified using various chromatographic approaches, including the HIC purification strategy described above. GFP purification has also become a pedagogical staple in biochemistry labs for the teaching of modern protein science techniques 12.
While basic HIC protein purification can be conducted using a substantially less robust chromatography system, the instrumentation presented here has a number of distinct advantages to aid in obtaining favorable results. Notable benefits of utilizing a highly automated system include improved run-to-run condition reproducibility, time-savings, and decreased opportunities for air to be introduced into the system 10. System-controlled buffer blending, which is facilitated by the system maximizer, allows for increased consistency in buffer preparation and experimental reproducibility. Drawing enough sample load into the dynamic sample loop for all scouting runs further ensures uniformity of the sample being added to each column and allows for sequential runs without interruption or manual reloading. Controlled sample injection from the sample loop onto the column decreases variability that may occur with manual sample loading. A pair of column selection valves allow for consecutive sample runs, each using a different HIC column, without having to replumb the system. Performing multi-wavelength analysis is particularly beneficial when assaying a protein with a unique spectrophotometric profile. In addition to GFP, cytochromes, flavoproteins, and other heme-containing proteins may benefit from this technique. Conductivity and pH monitoring devices allow for verification of real-time experimental conditions. Split fraction eluate collection allows for improved fraction handling and enables easy transfer for post-run analysis methods that require a minimal sample volume (e.g. ELISA, SDS-PAGE, western blot, and Experion microfluidic electrophoresis). While operating the second fraction collector offline requires manual synchronization, it allows for maximum flexibility in fraction collector selection. The most significant drawbacks to utilizing such a robust chromatography system for HIC column scouting and protein purification include the initial time and budgetary expenditures associated with instrument acquisition and operator training. 
The protocol presented here utilizes a Bio-Rad DuoFlow chromatography system; however, equally robust instrumentation from other manufacturers, such as the &Auml;KTA Avant from GE Healthcare, may also be utilized and are capable of producing equivalent results. Even comparable chromatography system have unique characteristics (e.g. method programming, component nomenclature, operator preference, and scalability limitations) that should be considered before initiating a purification procedure or instrument acquisition.

<table border="1">
<tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments (optional)</td>
 </tr>
 <tr>
 <td><a href="http://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=BRCatgProductDetail&productID=223301" target="_blank">BioLogic DuoFlow Pathfinder 20 System</a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="http://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=BRCatgProductDetail&productID=223301" target="_blank">7602257 </a></td>
 <td>Includes system maximizer, mixer, F10 workstation, AVR7-3 valve, QuadTec UV/Vis detector with flow cell, BioFrac fraction collector, BioLogic software, and starter kit</td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=760-0408&vertical=LSR&parentCategoryGUID=22c495f1-36ff-44a3-9140-ee7e54d0b1ba" target="_blank">AVR9-8 stream-select valve </a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=760-0408&vertical=LSR&parentCategoryGUID=22c495f1-36ff-44a3-9140-ee7e54d0b1ba" target="_blank">7600408 </a></td>
 <td>High-pressure valve, 9-port, 8-position, 3,500 psi (233 bar) limit, for use with BioLogic DuoFlow system</td>
 </tr>
 <tr>
 <td>Diverter valve SV3T-2 </td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td>7600410 </td>
 <td>Solenoid valve, 3-port, 2-position, 30 psi (2 bar) limit, for use with BioLogic DuoFlow system</td>
 </tr>
 <tr>
 <td>Stream splitter valve</td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=750-0451&vertical=LSR&parentCategoryGUID=22c495f1-36ff-44a3-9140-ee7e54d0b1ba" target="_blank">DynaLoop 25 Kit </a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=750-0451&vertical=LSR&parentCategoryGUID=22c495f1-36ff-44a3-9140-ee7e54d0b1ba" target="_blank">7500451 </a></td>
 <td>Sliding-piston sample loop kit, includes 25 ml DynaLoop sliding piston loop, DynaLoop parts kit (#750-0450) </td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/LSR/PDP/ec82e7b4-919e-428b-ac03-9adf1f50a48e/BioFractrade_Fraction_Collector" target="_blank">BioFrac Fraction Collector</a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/LSR/PDP/ec82e7b4-919e-428b-ac03-9adf1f50a48e/BioFractrade_Fraction_Collector" target="_blank">7410002</a></td>
 <td>Two fraction collectors used</td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=741-0088&vertical=LSR&parentCategoryGUID=ec82e7b4-919e-428b-ac03-9adf1f50a48e" target="_blank">BioFrac microplate drop head adapter</a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=741-0088&vertical=LSR&parentCategoryGUID=ec82e7b4-919e-428b-ac03-9adf1f50a48e" target="_blank">7410088</a></td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&vertical=LSR&country=US&lang=en&productID=741-0017" target="_blank">BioFrac microtiter plate adapter</a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&vertical=LSR&country=US&lang=en&productID=741-0017" target="_blank">7410017</a></td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=750-0202&vertical=LSR&parentCategoryGUID=c140016b-1958-4a91-be4c-8645a4c8204f" target="_blank">UV Optics Module </a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=750-0202&vertical=LSR&parentCategoryGUID=c140016b-1958-4a91-be4c-8645a4c8204f" target="_blank">7500202 </a></td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=760-1331&vertical=LSR&parentCategoryGUID=c4095dc1-9260-4431-b066-823b050048c8" target="_blank">Halogen lamp </a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=catProductDetail&isFromSearch=true&productID=760-1331&vertical=LSR&parentCategoryGUID=c4095dc1-9260-4431-b066-823b050048c8" target="_blank">7601331 </a></td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=BRCatgProductDetail&productID=220901" target="_blank">Econo Gradient Pump </a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=BRCatgProductDetail&productID=220901" target="_blank">7319001 </a></td>
 <td>gradient pump for low-pressure protein purification, includes tubing and fittings kit </td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=BRCatgProductDetail&productID=224301" target="_blank">Experion System </a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=BRCatgProductDetail&productID=224301" target="_blank">7007001 </a></td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=BRCatgProductDetail&productID=224101" target="_blank">Experion Pro260 Analysis Kit </a></td>
 <td><a href="http://www.bio-rad.com/" target="_blank">Bio-Rad</a></td>
 <td><a href="https://www.bio-rad.com/prd/en/US/adirect/biorad?cmd=BRCatgProductDetail&productID=224101" target="_blank">7007102 </a></td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>HiTrap HIC column selection kit</td>
 <td>GE Healthcare</td>
 <td>28-4110-07 </td>
 <td>Includes 7 x 1 ml pre-packed columns of HIC media for scouting</td>
 </tr>
 <tr>
 <td>GE Healthcare-to-Bio-Rad column fittings</td>
 <td>GE Healthcare</td>
 <td>18111251 and 18111257</td>
 <td>&nbsp;</td>
 </tr>
</tbody>
</table>

automated hydrophobic interaction chromatography column selection for use in protein purification

In contrast to other chromatographic methods for purifying proteins (e.g. gel filtration, affinity, and ion exchange), hydrophobic interaction chromatography (HIC) commonly requires experimental determination (referred to as screening or "scouting") in order to select the most suitable chromatographic medium for purifying a given protein 1. The method presented here describes an automated approach to scouting for an optimal HIC media to be used in protein purification.
HIC separates proteins and other biomolecules from a crude lysate based on differences in hydrophobicity. Similar to affinity chromatography (AC) and ion exchange chromatography (IEX), HIC is capable of concentrating the protein of interest as it progresses through the chromatographic process. Proteins best suited for purification by HIC include those with hydrophobic surface regions and able to withstand exposure to salt concentrations in excess of 2 M ammonium sulfate ((NH4)2SO4). HIC is often chosen as a purification method for proteins lacking an affinity tag, and thus unsuitable for AC, and when IEX fails to provide adequate purification. Hydrophobic moieties on the protein surface temporarily bind to a nonpolar ligand coupled to an inert, immobile matrix. The interaction between protein and ligand are highly dependent on the salt concentration of the buffer flowing through the chromatography column, with high ionic concentrations strengthening the protein-ligand interaction and making the protein immobile (i.e. bound inside the column) 2. As salt concentrations decrease, the protein-ligand interaction dissipates, the protein again becomes mobile and elutes from the column. Several HIC media are commercially available in pre-packed columns, each containing one of several hydrophobic ligands (e.g. S-butyl, butyl, octyl, and phenyl) cross-linked at varying densities to agarose beads of a specific diameter 3. Automated column scouting allows for an efficient approach for determining which HIC media should be employed for future, more exhaustive optimization experiments and protein purification runs 4.
The specific protein being purified here is recombinant green fluorescent protein (GFP); however, the approach may be adapted for purifying other proteins with one or more hydrophobic surface regions. GFP serves as a useful model protein, due to its stability, unique light absorbance peak at 397 nm, and fluorescence when exposed to UV light 5. Bacterial lysate containing wild type GFP was prepared in a high-salt buffer, loaded into a Bio-Rad DuoFlow medium pressure liquid chromatography system, and adsorbed to HiTrap HIC columns containing different HIC media. The protein was eluted from the columns and analyzed by in-line and post-run detection methods. Buffer blending, dynamic sample loop injection, sequential column selection, multi-wavelength analysis, and split fraction eluate collection increased the functionality of the system and reproducibility of the experimental approach.

Watch this Scientific Journal Video about Automated Hydrophobic Interaction Chromatography Column Selection for Use in Protein Purification at JoVE.com

Automated Hydrophobic Interaction Chromatography Column Selection for Use in Protein Purification

An automated method for identifying suitable hydrophobic interaction chromatography (HIC) media to be used in the process of protein purification is presented. The method utilizes a medium-pressure liquid chromatography system including automated buffer blending, dynamic sample loop injection, sequential column selection, multi-wavelength analysis, and split fraction eluate collection.

In contrast to other chromatographic methods for purifying proteins (e.g. gel filtration, affinity, and ion exchange), hydrophobic interaction ...

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43.1K Views.  Seattle University. An automated method for identifying suitable hydrophobic interaction chromatography (HIC) media to be used in the process of protein purification is presented. The method utilizes a medium-pressure liquid chromatography system including automated buffer blending, dynamic sample loop injection, sequential column selection, multi-wavelength analysis, and split fraction eluate collection.

Video: Automated Hydrophobic Interaction Chromatography Column Selection for Use in Protein Purification

Staining of Proteins in Gels with Coomassie G-250 without Organic Solvent and Acetic Acid

In classical protein staining protocols using Coomassie Brilliant Blue (CBB), solutions with high contents of toxic and flammable organic solvents (Methanol, Ethanol or 2-Propanol) and acetic acid are used for fixation, staining and destaining of proteins in a gel after SDS-PAGE. To speed up the procedure, heating the staining solution in the microwave oven for a short time is frequently used. This usually results in evaporation of toxic or hazardous Methanol, Ethanol or 2-Propanol and a strong smell of acetic acid in the lab which should be avoided due to safety considerations. In a protocol originally published in two patent applications by E.M. Wondrak (US2001046709 (A1), US6319720 (B1)), an alternative composition of the staining solution is described in which no organic solvent or acid is used. The CBB is dissolved in bidistilled water (60-80mg of CBB G-250 per liter) and 35 mM HCl is added as the only other compound in the staining solution. The CBB staning of the gel is done after SDS-PAGE and thorough washing of the gel in bidistilled water. By heating the gel during the washing and staining steps, the process can be finished faster and no toxic or hazardous compunds are evaporating. The staining of proteins occurs already within 1 minute after heating the gel in staining solution and is fully developed after 15-30 min with a slightly blue background that is destained completely by prolonged washing of the stained gel in bidistilled water, without affecting the stained protein bands.

A short protocol for protein staining with Coomassie Brilliant Blue (CBB) G-250 in polyacrylamide gels is described without using organic solvents or acetic acid as in the classical staining procedures with CBB.

In classical protein staining protocols using Coomassie Brilliant Blue (CBB), solutions with high contents of toxic and flammable organic solvents ...

Purification of the M. magneticum Strain AMB-1 Magnetosome Associated Protein MamA&Delta;41

Magnetotactic bacteria comprise a diverse group of aquatic microorganisms that are able to orientate themselves along geomagnetic fields. This behavior is believed to aid their search for suitable environments (1). This capability is conferred by the magnetosome, a subcellular organelle that consists of a linear-chain assembly of lipid vesicles each able to biomineralize and enclose a ~50-nm crystal of magnetite or greigite. A principle component of the magnetosome that was shown to be required for the formation of functional vesicles is MamA. MamA is a highly abundant magnetosome-associated protein which is one of the most characterized magnetosome-associated proteins in vivo (2-6). This article focuses on the purification of MamA, which despite being studied in vivo, no clear functional or structural details have been identified for it. Bioinformatics analysis suggested that MamA is a tetra-tricopeptide repeat (TPR) containing protein. TPR is a structural motif found as such or forming part of a bigger fold in a wide range of proteins, it serves as a template for protein-protein interactions and mediates multi-protein complexes (7). TPRs are involved in many crucial tasks in eukaryotic cell organelle processes and many bacterial pathways (8-14). In order to understand MamA, a unique TPR containing protein, highly purified protein is required as a first step. In this article, we present the purification protocol for a stable MamA deletion mutant (MamA&Delta;41) from M. magneticum AMB-1.

Purification of the &lt;em&gt;M. magneticum&lt;/em&gt; Strain AMB-1 Magnetosome Associated Protein MamA&amp;Delta;41

MamA is a unique Magnetosome associated protein which was shown to be involved in magnetosome activation. Here we present the purification protocol of MamA deletion mutant (MamA&Delta;41) from M. magneticum AMB-1.

Magnetotactic bacteria comprise a diverse group of aquatic microorganisms that are able to orientate themselves along geomagnetic fields. This behavior is ...

Bimolecular Fluorescence Complementation (BiFC) Assay for Protein-Protein Interaction in Onion Cells Using the Helios Gene Gun

Investigation of gene function in diverse organisms relies on knowledge of how the gene products interact with each other in their normal cellular environment. The Bimolecular Fluorescence Complementation (BiFC) Assay1 allows researchers to visualize protein-protein interactions in living cells and has become an essential research tool. This assay is based on the facilitated association of two fragments of a fluorescent protein (GFP) that are each fused to a potential interacting protein partner. The interaction of the two protein partners would facilitate the association of the N-terminal and C-terminal fragment of GFP, leading to fluorescence. For plant researchers, onion epidermal cells are an ideal experimental system for conducting the BiFC assay because of the ease in obtaining and preparing onion tissues and the direct visualization of fluorescence with minimal background fluorescence. The Helios Gene Gun (BioRad) is commonly used for bombarding plasmid DNA into onion cells. We demonstrate the use of Helios Gene Gun to introduce plasmid constructs for two interacting Arabidopsis thaliana transcription factors, SEUSS (SEU) and LEUNIG HOMOLOG (LUH)2 and the visualization of their interactions mediated by BiFC in onion epidermal cells.

Bimolecular Fluorescence Complementation BiFC Assay for Protein-Protein Interaction in Onion Cells Using the Helios Gene Gun

This article illustrates how to properly use the BioRad Helios Gene Gun to introduce plasmid DNA into onion epidermal cells and how to test for protein-protein interactions in onion cells based on the principle of Bimolecular Fluorescence Complementation (BiFC)

Investigation of gene function in diverse organisms relies on knowledge of how the gene products interact with each other in their normal cellular ...

Lipid Vesicle-mediated Affinity Chromatography using Magnetic Activated Cell Sorting (LIMACS): a Novel Method to Analyze Protein-lipid Interaction

The analysis of lipid protein interaction is difficult because lipids are embedded in cell membranes and therefore, inaccessible to most purification procedures. As an alternative, lipids can be coated on flat surfaces as used for lipid ELISA and Plasmon resonance spectroscopy. However, surface coating lipids do not form microdomain structures, which may be important for the lipid binding properties. Further, these methods do not allow for the purification of larger amounts of proteins binding to their target lipids.
 To overcome these limitations of testing lipid protein interaction and to purify lipid binding proteins we developed a novel method termed lipid vesicle-mediated affinity chromatography using magnetic-activated cell sorting (LIMACS). In this method, lipid vesicles are prepared with the target lipid and phosphatidylserine as the anchor lipid for Annexin V MACS. Phosphatidylserine is a ubiquitous cell membrane phospholipid that shows high affinity to the protein Annexin V. Using magnetic beads conjugated to Annexin V the phosphatidylserine-containing lipid vesicles will bind to the magnetic beads. When the lipid vesicles are incubated with a cell lysate the protein binding to the target lipid will also be bound to the beads and can be co-purified using MACS. This method can also be used to test if recombinant proteins reconstitute a protein complex binding to the target lipid. 
 We have used this method to show the interaction of atypical PKC (aPKC) with the sphingolipid ceramide and to co-purify prostate apoptosis response 4 (PAR-4), a protein binding to ceramide-associated aPKC. We have also used this method for the reconstitution of a ceramide-associated complex of recombinant aPKC with the cell polarity-related proteins Par6 and Cdc42. Since lipid vesicles can be prepared with a variety of sphingo- or phospholipids, LIMACS offers a versatile test for lipid-protein interaction in a lipid environment that resembles closely that of the cell membrane. Additional lipid protein complexes can be identified using proteomics analysis of lipid binding protein co-purified with the lipid vesicles.

Lipid Vesicle-mediated Affinity Chromatography using Magnetic Activated Cell Sorting LIMACS: a Novel Method to Analyze Protein-lipid Interaction

To test the interaction of a protein with its target lipid we used MACS and Annexin V-conjugated magnetic beads and lipid vesicles synthesized from the target lipid and Annexin V-binding phosphatidylserine. Proteins bound to the target lipid are co-purified and analyzed after elution from the beads.

The analysis of lipid protein interaction is difficult because lipids are embedded in cell membranes and therefore, inaccessible to most purification ...

Purification of Hsp104, a Protein Disaggregase

Hsp104 is a hexameric AAA+ protein1 from yeast, which couples ATP hydrolysis to protein disaggregation2-10 (Fig. 1). This activity imparts two key selective advantages. First, renaturation of disordered aggregates by Hsp104 empowers yeast survival after various protein-misfolding stresses, including heat shock3,5,11,12. Second, remodeling of cross-beta amyloid fibrils by Hsp104 enables yeast to exploit myriad prions (infectious amyloids) as a reservoir of beneficial and heritable phenotypic variation13-22. Remarkably, Hsp104 directly remodels preamyloid oligomers and amyloid fibrils, including those comprised of the yeast prion proteins Sup35 and Ure223-30. This amyloid-remodeling functionality is a specialized facet of yeast Hsp104. The E. coli orthologue, ClpB, fails to remodel preamyloid oligomers or amyloid fibrils26,31,32.
Hsp104 orthologues are found in all kingdoms of life except, perplexingly, animals. Indeed, whether animal cells possess any enzymatic system that couples protein disaggregation to renaturation (rather than degradation) remains unknown33-35. Thus, we and others have proposed that Hsp104 might be developed as a therapeutic agent for various neurodegenerative diseases connected with the misfolding of specific proteins into toxic preamyloid oligomers and amyloid fibrils4,7,23,36-38. There are no treatments that directly target the aggregated species associated with these diseases. Yet, Hsp104 dissolves toxic oligomers and amyloid fibrils composed of alpha-synuclein, which are connected with Parkinson's Disease23 as well as amyloid forms of PrP39. Importantly, Hsp104 reduces protein aggregation and ameliorates neurodegeneration in rodent models of Parkinson's Disease23 and Huntington's disease38. Ideally, to optimize therapy and minimize side effects, Hsp104 would be engineered and potentiated to selectively remodel specific aggregates central to the disease in question4,7. However, the limited structural and mechanistic understanding of how Hsp104 disaggregates such a diverse repertoire of aggregated structures and unrelated proteins frustrates these endeavors30,40-42.
To understand the structure and mechanism of Hsp104, it is essential to study the pure protein and reconstitute its disaggregase activity with minimal components. Hsp104 is a 102kDa protein with a pI of ~5.3, which hexamerizes in the presence of ADP or ATP, or at high protein concentrations in the absence of nucleotide43-46. Here, we describe an optimized protocol for the purification of highly active, stable Hsp104 from E. coli. The use of E. coli allows simplified large-scale production and our method can be performed quickly and reliably for numerous Hsp104 variants. Our protocol increases Hsp104 purity and simplifies His6-tag removal compared to a previous purification method from E. coli47. Moreover, our protocol is more facile and convenient than two more recent protocols26,48.

Here, we describe a protocol for the purification of highly active Hsp104, a hexameric AAA+ protein from yeast, which couples ATP hydrolysis to protein disaggregation. This scheme exploits a His6-tagged construct for affinity purification from E. coli followed by anion-exchange chromatography, His6-tag removal with TEV protease, and size-exclusion chromatography.

Hsp104 is a hexameric AAA+ protein1 from yeast, which couples ATP hydrolysis to protein disaggregation2-10 (Fig. 1). This activity imparts two key ...

A Protocol for Phage Display and Affinity Selection Using Recombinant Protein Baits

Using recombinant phage as a scaffold to present various protein portions encoded by a directionally cloned cDNA library to immobilized bait molecules is an efficient means to discover interactions. The technique has largely been used to discover protein-protein interactions but the bait molecule to be challenged need not be restricted to proteins. The protocol presented here has been optimized to allow a modest number of baits to be screened in replicates to maximize the identification of independent clones presenting the same protein. This permits greater confidence that interacting proteins identified are legitimate interactors of the bait molecule. Monitoring the phage titer after each affinity selection round provides information on how the affinity selection is progressing as well as on the efficacy of negative controls. One means of titering the phage, and how and what to prepare in advance to allow this process to progress as efficiently as possible, is presented. Attributes of amplicons retrieved following isolation of independent plaque are highlighted that can be used to ascertain how well the affinity selection has progressed. Trouble shooting techniques to minimize false positives or to bypass persistently recovered phage are explained. Means of reducing viral contamination flare up are discussed.

Phage display is a powerful technique to capture proteins or protein moieties that interact with an immobilized molecule of interest. Once a decision of the type of phage cDNA library to create and screen has been made, the protocol described here permits efficient affinity selection leading to identification of interactors.

Using  recombinant phage as a scaffold to present various protein portions encoded by  a directionally cloned cDNA library to immobilized bait molecules ...

Identifying Protein-protein Interaction in Drosophila Adult Heads by Tandem Affinity Purification (TAP)

Genetic screens conducted using Drosophila melanogaster (fruit fly) have made numerous milestone discoveries in the advance of biological sciences. However, the use of biochemical screens aimed at extending the knowledge gained from genetic analysis was explored only recently. Here we describe a method to purify the protein complex that associates with any protein of interest from adult fly heads. This method takes advantage of the Drosophila GAL4/UAS system to express a bait protein fused with a Tandem Affinity Purification (TAP) tag in fly neurons in vivo, and then implements two rounds of purification using a TAP procedure similar to the one originally established in yeast1 to purify the interacting protein complex. At the end of this procedure, a mixture of multiple protein complexes is obtained whose molecular identities can be determined by mass spectrometry. Validation of the candidate proteins will benefit from the resource and ease of performing loss-of-function studies in flies. Similar approaches can be applied to other fly tissues. We believe that the combination of genetic manipulations and this proteomic approach in the fly model system holds tremendous potential for tackling fundamental problems in the field of neurobiology and beyond.

Identifying Protein-protein Interaction in Drosophila Adult Heads by Tandem Affinity Purification TAP

Drosophila is famous for its powerful genetic manipulation, but not for its suitability of in-depth biochemical analysis. Here we present a TAP-based procedure to identify interacting partners of any protein of interest from the fly brain. This procedure can potentially lead to new avenues of research.

Genetic screens conducted using Drosophila melanogaster (fruit fly) have made numerous milestone discoveries in the advance of biological sciences. ...

Identifying Protein-protein Interaction Sites Using Peptide Arrays

Protein-protein interactions mediate most of the processes in the living cell and control homeostasis of the organism. Impaired protein interactions may result in disease, making protein interactions important drug targets. It is thus highly important to understand these interactions at the molecular level. Protein interactions are studied using a variety of techniques ranging from cellular and biochemical assays to quantitative biophysical assays, and these may be performed either with full-length proteins, with protein domains or with peptides. Peptides serve as excellent tools to study protein interactions since peptides can be easily synthesized and allow the focusing on specific interaction sites. Peptide arrays enable the identification of the interaction sites between two proteins as well as screening for peptides that bind the target protein for therapeutic purposes. They also allow high throughput SAR studies. For identification of binding sites, a typical peptide array usually contains partly overlapping 10-20 residues peptides derived from the full sequences of one or more partner proteins of the desired target protein. Screening the array for binding the target protein reveals the binding peptides, corresponding to the binding sites in the partner proteins, in an easy and fast method using only small amount of protein.
In this article we describe a protocol for screening peptide arrays for mapping the interaction sites between a target protein and its partners. The peptide array is designed based on the sequences of the partner proteins taking into account their secondary structures. The arrays used in this protocol were Celluspots arrays prepared by INTAVIS Bioanalytical Instruments. The array is blocked to prevent unspecific binding and then incubated with the studied protein. Detection using an antibody reveals the binding peptides corresponding to the specific interaction sites between the proteins.

Peptide array screening is a high throughput assay for identifying protein-protein interaction sites. This allows mapping multiple interactions of a target protein and can serve as a method for identifying sites for inhibitors that target a protein. Here we describe a protocol for screening and analyzing peptide arrays.

Protein-protein interactions mediate most of the processes in the living cell and control homeostasis of the organism. Impaired protein interactions may ...

Genome-wide Protein-protein Interaction Screening by Protein-fragment Complementation Assay (PCA) in Living Cells

Proteins are the building blocks, effectors and signal mediators of cellular processes. A protein&#8217;s function, regulation and localization often depend on its interactions with other proteins. Here, we describe a protocol for the yeast protein-fragment complementation assay (PCA), a powerful method to detect direct and proximal associations between proteins in living cells. The interaction between two proteins, each fused to a dihydrofolate reductase (DHFR) protein fragment, translates into growth of yeast strains in presence of the drug methotrexate (MTX). Differential fitness, resulting from different amounts of reconstituted DHFR enzyme, can be quantified on high-density colony arrays, allowing to differentiate interacting from non-interacting bait-prey pairs. The high-throughput protocol presented here is performed using a robotic platform that parallelizes mating of bait and prey strains carrying complementary DHFR-fragment fusion proteins and the survival assay on MTX. This protocol allows to systematically test for thousands of protein-protein interactions (PPIs) involving bait proteins of interest and offers several advantages over other PPI detection assays, including the study of proteins expressed from their endogenous promoters without the need for modifying protein localization and for the assembly of complex reporter constructs.

Genome-wide Protein-protein Interaction Screening by Protein-fragment Complementation Assay PCA in Living Cells

Proteins interact with each other and these interactions determine in a large part their functions. Protein interaction partners can be identified at high-throughput in vivo using a yeast fitness assay based on the dihydrofolate reductase protein-fragment complementation assay (DHFR-PCA).

Proteins are the building blocks, effectors and signal mediators of cellular processes. A protein&#8217;s function, regulation and localization often ...

Luciferase Complementation Imaging Assay in Nicotiana benthamiana Leaves for Transiently Determining Protein-protein Interaction Dynamics

Protein-protein interactions are fundamental mechanisms for relaying signal transduction in most cellular processes; therefore, identification of novel protein-protein interaction pairs and monitoring protein interaction dynamics are of particular interest for revealing how plants respond to environmental factors and/or developmental signals. A plethora of approaches have been developed to examine protein-protein interactions, either in vitro or in vivo. Among them, the recently established luciferase complementation imaging (LCI) assay is the simplest and fastest method for demonstrating in vivo protein-protein interactions. In this assay, protein A or protein B is fused with the amino-terminal or carboxyl-terminal half of luciferase, respectively. When protein A interacts with protein B, the two halves of luciferase will be reconstituted to form a functional and active luciferase enzyme. Luciferase activity can be recorded with a luminometer or CCD-camera. Compared with other approaches, the LCI assay shows protein-protein interactions both qualitatively and quantitatively. Agrobacterium infiltration in Nicotiana benthamiana leaves is a widely used system for transient protein expression. With the combination of LCI and transient expression, these approaches show that the physical interaction between COP1 and SPA1 was gradually reduced after jasmonate treatment.

Luciferase Complementation Imaging Assay in Nicotiana benthamiana Leaves for Transiently Determining Protein-protein Interaction Dynamics

This manuscript describes an easy and rapid experimental procedure for determining protein-protein interactions based on the measurement of luciferase activity.

Protein-protein interactions are fundamental mechanisms for relaying signal transduction in most cellular processes; therefore, identification of novel ...