The authors wish to thank Mr. Luis F. Delgadillo (Department of Chemical and Biomolecular Engineering, Ohio University), Mr. Matthew H. Williams (Department of Chemical and Biomolecular Engineering, Ohio University), and Dr. Filiberto Cedeno-Laurent (Brigham and Women&#8217;s Hospital and Harvard Medical School) for expert technical assistance.&#160;The authors also wish to thank the Winter 2011 CHE 404/BME 504 and Fall 2012 CHE 4830/BME 5830 students (Department of Chemical and Biomolecular Engineering and Biomedical Engineering Program, Ohio University) for technical advice and discussion. This work was supported by National Science Foundation (NSF) Major Research Instrumentation grant CBET-1039869 (MMB), NSF CBET-1106118 (MMB), Dermatology Foundation Research Grant A050422 (SRB), National Institutes of Health (NIH) NCI grant 1R15CA161830-01 (MMB), NIH Kirschstein-NRSA Postdoctoral Fellowship F32CA144219-01A1 (SRB), NIH/NCI R01CA173610 (CJD),&#160;and NIH NCCAM grant R01AT004628 (CJD).

1. Verify the Affinity for Protein A
<ol>
	<li>Verify that the Fc-expressing protein (recombinant fusion protein or IgG antibody, heretofore referred to as "protein") has acceptable affinity for protein A14-17 prior to using the protein A membrane adsorber, and test for the presence of the protein in the stock solution (e.g. cell culture supernatant clarified by centrifugation at 1,000 x g for 5 min to pellet suspended cells). Use flow cytometry, Western blotting, ELISA, etc. to detect protein function and/or presence of Fc, based on lab preference. Ideally, quantify the protein in the cell culture supernatant (step 6) to avoid exceeding protein A membrane adsorber capacity. Proceed if protein is detected.</li>
</ol>
2. Prepare Protein A Membrane Adsorber and Cell Culture Supernatant
<ol>
	<li>Follow the manufacturer's instructions for preparing the membrane adsorber. Never let air enter the membrane adsorber. All solutions perfused through the membrane adsorber should be at room temperature and prefiltered using a 0.22 &#181;m filter. Fill a 10 ml syringe with 0.22 &#181;m-filtered Dulbecco's phosphate buffered saline (DPBS) or buffer of choice and discharge air bubbles. Perfuse DPBS to remove the storage solution and to equilibrate the membrane adsorber immediately before use.</li>
	<li>Filter the cell culture supernatant immediately before perfusion through the membrane adsorber, using a vacuum-driven 0.22 &#181;m sterile filtration unit.</li>
</ol>
3. Load the Protein A Membrane Adsorber
<ol>
	<li>Aspirate cell culture supernatant into a Luer Lock syringe (30 ml or larger), and discharge any air bubbles.</li>
	<li>Assemble materials and equipment as shown in Figure 1. Connect the syringe to the inlet of the membrane adsorber. Attach flexible tubing to the membrane adsorber outlet. If desired, place a 0.22 &#181;m syringe filter between the syringe and the membrane adsorber. Use a flask or bottle to catch flow through (also known as filtrate), from the adsorber.</li>
	<li>Set the syringe pump to the desired volumetric flow rate, but do not exceed the manufacturer's recommended flow rate (e.g. 10 ml/min). Perfuse the cell culture supernatant through the membrane adsorber, collecting flow through in a beaker or other container. Reload the syringe with supernatants needed.</li>
	<li>If desired, test the flow through for the presence of protein using flow cytometry, Western blotting, ELISA, etc. based on lab preference. It is typically unnecessary to reperfuse the flow through.</li>
</ol>
4. Elute Protein from the Membrane Adsorber
<ol>
	<li>Wash the membrane adsorber with 10 ml DPBS to remove any nonbound protein.</li>
	<li>Elute protein from the membrane adsorber at the desired flow rate (e.g. 1 ml/min) using 10-15 ml of elution buffer (e.g. amine-based elution buffer (pH 2.8)). Catch eluate in a tube containing neutralizing buffer (e.g. 1 M Tris (pH 9.4)) at 10% of elution volume (1.0-1.5 ml).</li>
	<li>Alternatively, elute protein in one ml increments into tubes containing 100 &#181;l of neutralization buffer, using a total volume of 10-15 ml elution buffer. Use the preferred characterization method to test each fraction for the presence of protein.</li>
	<li>Regenerate the membrane adsorber according to the manufacturer's instructions. Perfuse 10 ml of 0.22 &#181;m-filtered DPBS or buffer of choice, then 10 ml of 0.22 &#181;m-filtered 50 mM NaOH in 1 N NaCl, and finally 10 ml of 0.22 &#181;m-filtered DPBS. Fill the membrane adsorber with 20% ethanol in DPBS for long-term storage at 4 &#186;C.</li>
</ol>
5. Concentrate and Dialyze the Protein
<ol>
	<li>Deposit all eluate (or elution fractions containing protein as determined in step 4.3) in a 10 kDa molecular weight cut-off centrifugal filter unit. Follow the manufacturer's instructions for centrifugation.</li>
	<li>Dialyze the retentate in a small volume dialysis unit (10 kDa molecular weight cut-off) against the buffer of choice, following the manufacturer's instructions. Buffer may need to be added to dialyzed material if protein precipitation is a concern. If desired, the dialyzed material can be refrigerated until step 6 can be performed, but long term storage without preservatives is not recommended.</li>
</ol>
6. Quantify and Characterize Purified Product in an Expedited Western Blotting Procedure
<ol>
	<li>Resolve purified protein and Fc standards on the gel of choice by SDS-PAGE, under reducing or nonreducing conditions as desired18-20. Use a mini gel rather than midi gel to minimize run time.
		<ol>
			<li>If not already known, determine the Fc standards range over which band signal varies linearly with respect to quantity of loaded (e.g. 0.1-1 mg). Use the same gel, running conditions, transfer conditions, and reagents that will be used to quantify and characterize purified protein.</li>
			<li>Load multiple sample amounts of purified protein, including samples diluted with DPBS, to ensure that the purified protein band signals are within the linear signal range of Fc standards in image analysis.</li>
		</ol>
	</li>
	<li>Transfer proteins from the gel to a polyvinylidene fluoride (PVDF) membrane in a discontinuous buffer system using a semidry blotter13, following the blotter manufacturer's instructions. Transfer time is typically 5-10 min. If desired, Coomassie stain the gel after transfer to verify transfer efficiency21.</li>
	<li>Perform immunoblotting with anti-Fc or anti-IgG conjugated to alkaline phosphatase (AP) or horse radish peroxidase (HRP), based on lab preference, using a vacuum-assisted protein detection system. Immunoblotting time is typically less than 1 hr.</li>
	<li>Develop immunoblot using the substrate and method of choice (e.g. AP substrate and enhanced chemiluminescence).</li>
	<li>Quantify purified protein by image analysis. Perform a linear regression on the band signals from Fc standards. If R2&#62;0.90, use the equation for the line to calculate protein quantity from its band signal(s). Account for sample dilution if necessary. Since quantification of the protein is performed on the basis of Fc, adjust the value for molecular weight differences between the protein and Fc. If R2&#60;0.90, repeat step 6 in its entirety.</li>
	<li>Validate protein using functional assays or methods to detect Fc via flow cytometry, Western blotting, ELISA, etc. based on lab preference.</li>
	<li>Dilute protein to desired concentration and/or add any desired preservatives or stabilizers to the purified protein solution before aliquoting for long-term storage, frozen or otherwise.</li>
</ol>

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There is nothing to disclose.

The protocol described herein was developed to rapidly isolate and characterize a chimeric fusion protein expressing human Fc (Gal-1hFc), without significantly compromising product recovery or inflating cost.&#160;The key components of the streamlined workflow are a protein A membrane adsorber for isolation, and semidry transfer and vacuum-assisted immunoblotting for characterization by Western blotting.
The dramatic decrease in processing time for isolation and characterization of Gal-1hFc fr...

Isolation of antibodies and recombinant proteins expressing immunoglobulin G (IgG) Fc fragments from cell culture supernatants and dilute lysed cell solutions can be accomplished using protein A affinity chromatography. In basic science and engineering laboratories and industry, columns packed with porous protein A-coated agarose, glass, or polymeric beads are most commonly used for affinity chromatography, despite high financial costs and long processing times1-3. It is well-appreciated that affinity chromatography represents the largest expense and processing bottleneck in both lab and industrial settings2,4. As a result, numerous improvements have been developed to decrease cost and processing time without sacrificing overall product recovery from the process train1,2,5-7. Particularly promising for the isolation of antibodies and other Fc-expressing proteins is affinity chromatography using a protein A membrane adsorber2,5,7-10. Whereas Fc capture in column chromatography is diffusion-limited (i.e.&#160;the Fc-expressing protein must diffuse into and through internal pores to reach the majority of the protein A) with high pressure drop across the column, mass transport in membrane adsorbers is driven by bulk convection, resulting in avoidance of diffusion limitations8,9,11,12. In addition, pressure drop across the membrane adsorber is low, thereby permitting faster perfusion flow rates compared to bead-packed columns8,9,11,12. Thus, for laboratory scale isolation, membrane chromatography is predicted to reduce isolation time by several hours and increase product capture compared to column chromatography. Furthermore, mathematical models for IgG adsorption in membrane adsorbers have been proposed8,9,11,12, thus allowing end-users to predict performance in the lab.
Another bottleneck in basic science and engineering laboratories is the characterization of the Fc-expressing protein. However, selection of appropriate methods to complete characterization assays, such Western blots, can greatly reduce time spent on product testing.&#160;For instance, semidry transfer in a discontinuous buffer system can accomplish electrophoretic transfer of proteins from an SDS-PAGE gel to a polyvinyl difluoridine (PVDF) membrane in a matter of minutes, as opposed to 1-2 hr in tank (wet) transfer in a continuous buffer system13.
A rapid, inexpensive, and effective protocol to isolate and characterize a chimeric fusion protein expressing an Fc fragment of human IgG is described herein. Most equipment is readily available in standard basic biomedical science, biology, chemistry, and (bio)chemical engineering labs, and all reagents are commercially available.&#160;Although representative results were generated from the isolation and characterization of a murine galectin-1/human Fc chimeric fusion protein (Gal-1hFc), the streamlined protocol can be applied to the isolation of other molecules that possess an Fc fragment, such as antibodies, Fc fragments themselves, or other Fc fusion proteins.&#160;Our improvements dramatically decreased processing time (as few as 4 hr but more typically ~9 hr, compared to 20+ work hours) while achieving similar or improved product recovery compared to standard methods.

<table border="0" cellpadding="0" cellspacing="0" width="822">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:313px;">Protein A membrane adsorber (Sartobind Protein A 2 ml)&#160;</td>
			<td style="width:191px;">Sartorius-Stedim</td>
			<td style="width:147px;">93PRAP06HB-12--A</td>
			<td style="width:173px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Amicon Ultra centrifugal filter, 10 kDa, 4 ml</td>
			<td style="width:191px;">Millipore</td>
			<td>UFC801008</td>
			<td>Use 15 ml volume if needed</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Sterile vacuum filter unit, 0.22 &#181;m, 500 ml</td>
			<td>Millipore</td>
			<td>SCGPU05RE</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">10 ml Syringes with Luer Lock tips</td>
			<td>BD</td>
			<td>301604</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">30 ml Syringes with&#160; Luer Lock tips</td>
			<td>BD</td>
			<td>309650</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Tygon lab tubing (1/16 in x 1/8 in x 50 ft)</td>
			<td>Cole Parmer</td>
			<td>WU-95903-16</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:313px;">Slide-A-Lyzer MINI Dialysis Devices (10K MWCO)</td>
			<td>Thermo Scientific</td>
			<td>69576</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Snap i.d. antibody collection tray</td>
			<td>EMD Millipore</td>
			<td>WBAVDABTR</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Snap i.d. single well blot holder</td>
			<td>EMD Millipore</td>
			<td>WBAVDBH01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Elution buffer</td>
			<td>Thermo Scientific</td>
			<td>21004</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Tris, ultra pure</td>
			<td>Fisher Scientific</td>
			<td>819623</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Sodium chloride</td>
			<td>Fisher Scientific</td>
			<td>7647-14-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Tween 20</td>
			<td>Fisher Scientific</td>
			<td>BP337-100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">DPBS</td>
			<td>Thermo Scientific&#160;</td>
			<td>SH30028.02</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:313px;">DPBS with Ca2+/Mg2+</td>
			<td>Life Technologies</td>
			<td>14080-055</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">BSA</td>
			<td>Sigma</td>
			<td>A9647</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Human Fc</td>
			<td>Bethyl Research Laboratories</td>
			<td>&#160;P80-104</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Anti-human Fc-APC</td>
			<td>Jackson Immunoresearch</td>
			<td>109136170</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Anti-human Fc-AP</td>
			<td>Bio-Rad</td>
			<td>170-5018</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Alkaline phosphatase substrate</td>
			<td>Promega</td>
			<td style="width:147px;">S3841</td>
			<td style="width:173px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:313px;">Flow cytometry tubes (5 ml polystyrene or polypropylene)</td>
			<td>BD</td>
			<td>352054</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;"></td>
			<td style="width:191px;"></td>
			<td style="width:147px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:313px;">Name of Material/ Equipment</td>
			<td style="width:191px;">Company</td>
			<td style="width:147px;">Catalog Number</td>
			<td>Comments/Description</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Syringe pump</td>
			<td>Harvard Apparatus</td>
			<td>55-2226</td>
			<td style="width:173px;">A peristaltic pump is also acceptable</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;">Protein gel electrophoresis system&#160;</td>
			<td>Bio-Rad Laboratories</td>
			<td>552BR094876</td>
			<td style="width:173px;">Any gel electrophoresis system is acceptable, but mini gel systems run fastest</td>
		</tr>
		<tr height="126">
			<td height="126" style="height:126px;">Semidry blotter&#160;</td>
			<td>Bio-Rad Laboratories</td>
			<td style="width:147px;">690BR006163</td>
			<td style="width:173px;">Any transfer system is acceptable, but discontinuos transfer systems perform electrophoretic transfer fastest</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:313px;">SNAP i.d. vacuum-assisted protein detection system</td>
			<td style="width:191px;">EMD Millipore</td>
			<td>WBAVDBASE</td>
			<td style="width:173px;">An upgraded model has replaced this specific instrument, but either should work just as well</td>
		</tr>
	</tbody>
</table>

isolation and characterization of chimeric human fc-expressing proteins using protein a membrane adsorbers and a streamlined workflow

Laboratory scale to industrial scale purification of biomolecules from cell culture supernatants and lysed cell solutions can be accomplished using affinity chromatography.&#160;While affinity chromatography using porous protein A agarose beads packed in columns is arguably the most common method of laboratory scale isolation of antibodies and recombinant proteins expressing Fc fragments of IgG, it can be a time consuming and expensive process.&#160;Time and financial constraints are especially daunting in small basic science labs that must recover hundreds of micrograms to milligram quantities of protein from dilute solutions, yet lack access to high pressure liquid delivery systems and/or personnel with expertise in bioseparations. Moreover, product quantification and characterization may also excessively lengthen processing time over several workdays and inflate expenses (consumables, wages, etc.).&#160;Therefore, a fast, inexpensive, yet effective protocol is needed for laboratory scale isolation and characterization of antibodies and other proteins possessing an Fc fragment.&#160;To this end, we have devised a protocol that can be completed by limited-experience technical staff in less than 9 hr (roughly one workday) and as quickly as 4 hr, as opposed to traditional methods that demand 20+ work hours. Most required equipment is readily available in standard biomedical science, biochemistry, and (bio)chemical engineering labs, and all reagents are commercially available.&#160;To demonstrate this protocol, representative results are presented in which chimeric&#160;murine galectin-1 fused to human Fc (Gal-1hFc) from cell culture supernatant was isolated using a protein A membrane adsorber.&#160;Purified Gal-1hFc was quantified using an expedited Western blotting analysis procedure and characterized using flow cytometry. The streamlined workflow can be modified for other Fc-expressing proteins, such as antibodies, and/or altered to incorporate alternative quantification and characterization methods.

The streamlined protocol for isolation and characterization of Fc-expressing proteins is routinely used to process chimeric murine galectin-1 fused to human Fc (Gal-1hFc) from dilute cell culture supernatants. The flowchart in Figure 2 illustrates the workflow and time for each step in the protocol. For a typical batch of 300 ml of supernatant, the total processing time is approximately 9 hr when the optional flow cytometry testing of elution fractions is performed. If all flow cytometry analysis is omit...

Watch this Scientific Journal Video about Isolation and Characterization Of Chimeric Human Fc-expressing Proteins Using Protein A Membrane Adsorbers And A Streamlined Workflow at JoVE.com

Isolation and Characterization Of Chimeric Human Fc-expressing Proteins Using Protein A Membrane Adsorbers And A Streamlined Workflow

Compared with traditional affinity chromatography using protein A agarose bead-packed columns, protein A membrane adsorbers can significantly speed laboratory-scale isolation of antibodies and other Fc fragment-expressing proteins.&#160;Appropriate analysis and quantification methods can further accelerate protein processing, allowing isolation/characterization to be completed in one workday, instead of 20+ work hours.

Laboratory scale to industrial scale purification of biomolecules from cell culture supernatants and lysed cell solutions can be accomplished using ...

isolation-characterization-chimeric-human-fc-expressing-proteins

Research

JoVE Journal

Bioengineering

7.0K Views.  Ohio University. Compared with traditional affinity chromatography using protein A agarose bead-packed columns, protein A membrane adsorbers can significantly speed laboratory-scale isolation of antibodies and other Fc fragment-expressing proteins. Appropriate analysis and quantification methods can further accelerate protein processing, allowing isolation/characterization to be completed in one workday, instead of 20+ work hours.

Video: Isolation and Characterization Of Chimeric Human Fc-expressing Proteins Using Protein A Membrane Adsorbers And A Streamlined Workflow

Creating Two-Dimensional Patterned Substrates for Protein and Cell Confinement

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1 While microcontact printing can be employed to directly print a large number of molecules, including proteins,2 DNA,3 and silanes,4 the formation of self-assembled monolayers (SAMs) from long chain alkane thiols on gold provides a simple way to confine proteins and cells to specific patterns containing adhesive and resistant regions. This confinement can be used to control cell morphology and is useful for examining a variety of questions in protein and cell biology. Here, we describe a general method for the creation of well-defined protein patterns for cellular studies.5 This process involves three steps: the production of a patterned master using photolithography, the creation of a PDMS stamp, and microcontact printing of a gold-coated substrate. Once patterned, these cell culture substrates are capable of confining proteins and/or cells (primary cells or cell lines) to the pattern.
The use of self-assembled monolayer chemistry allows for precise control over the patterned protein/cell adhesive regions and non-adhesive regions; this cannot be achieved using direct protein stamping. Hexadecanethiol, the long chain alkane thiol used in the microcontact printing step, produces a hydrophobic surface that readily adsorbs protein from solution. The glycol-terminated thiol, used for backfilling the non-printed regions of the substrate, creates a monolayer that is resistant to protein adsorption and therefore cell growth.6 These thiol monomers produce highly structured monolayers that precisely define regions of the substrate that can support protein adsorption and cell growth. As a result, these substrates are useful for a wide variety of applications from the study of intercellular behavior7 to the creation of microelectronics.8
While other types of monolayer chemistry have been used for cell culture studies, including work from our group using trichlorosilanes to create patterns directly on glass substrates,9 patterned monolayers formed from alkane thiols on gold are straight-forward to prepare. Moreover, the monomers used for monolayer preparation are commercially available, stable, and do not require storage or handling under inert atmosphere. Patterned substrates prepared from alkane thiols can also be recycled and reused several times, maintaining cell confinement.10

Self-assembled monolayers (SAMs) formed from long chain alkane thiols on gold provide well-defined substrates for the formation of protein patterns and cell confinement. Microcontact printing of hexadecanethiol using a polydimethylsiloxane (PDMS) stamp followed by backfilling with a glycol-terminated alkane thiol monomer produces a pattern where protein and cells adsorb only to the stamped hexadecanethiol region.

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1  While microcontact printing ...

Detection and Isolation of Circulating Melanoma Cells using Photoacoustic Flowmetry

Circulating tumor cells (CTCs) are those cells that have separated from a macroscopic tumor and spread through the blood and lymph systems to seed secondary tumors1,2,3. CTCs are indicators of metastatic disease and their detection in blood samples may be used to diagnose cancer and monitor a patient&prime;s response to therapy. Since CTCs are rare, comprising about one tumor cell among billions of normal blood cells in advanced cancer patients, their detection and enumeration is a difficult task. We exploit the presence of pigment in most melanoma cells to generate photoacoustic, or laser induced ultrasonic waves in a custom flow cytometer for detection of circulating melanoma cells (CMCs)4,5. This process entails separating a whole blood sample using centrifugation and obtaining the white blood cell layer. If present in whole blood, CMCs will separate with the white blood cells due to similar density. These cells are resuspended in phosphate buffered saline (PBS) and introduced into the flowmeter. Rather than a continuous flow of the blood cell suspension, we induced two phase flow in order to capture these cells for further study. In two phase flow, two immiscible liquids in a microfluidic system meet at a junction and form alternating slugs of liquid6,7. PBS suspended white blood cells and air form microliter slugs that are sequentially irradiated with laser light. The addition of a surfactant to the liquid phase allows uniform slug formation and the user can create different sized slugs by altering the flow rates of the two phases. Slugs of air and slugs of PBS with white blood cells contain no light absorbers and hence, do not produce photoacoustic waves. However, slugs of white blood cells that contain even single CMCs absorb laser light and produce high frequency acoustic waves. These slugs that generate photoacoustic waves are sequestered and collected for cytochemical staining for verification of CMCs.

We have developed a flow cytometer using laser induced ultrasound to detect circulating melanoma cells as an early indicator of metastatic disease.

Circulating tumor cells (CTCs) are those cells that have separated from a macroscopic tumor and spread through the blood and lymph systems to seed ...

Membrane-SPINE: A Biochemical Tool to Identify Protein-protein Interactions of Membrane Proteins In Vivo

Membrane proteins are essential for cell viability and are therefore important therapeutic targets1-3. Since they function in complexes4, methods to identify and characterize their interactions are necessary5. To this end, we developed the Membrane Strep-protein interaction experiment, called Membrane-SPINE6. This technique combines in vivo cross-linking using the reversible cross-linker formaldehyde with affinity purification of a Strep-tagged membrane bait protein. During the procedure, cross-linked prey proteins are co-purified with the membrane bait protein and subsequently separated by boiling. Hence, two major tasks can be executed when analyzing protein-protein interactions (PPIs) of membrane proteins using Membrane-SPINE: first, the confirmation of a proposed interaction partner by immunoblotting, and second, the identification of new interaction partners by mass spectrometry analysis. Moreover, even low affinity, transient PPIs are detectable by this technique. Finally, Membrane-SPINE is adaptable to almost any cell type, making it applicable as a powerful screening tool to identify PPIs of membrane proteins.

Membrane-SPINE: A Biochemical Tool to Identify Protein-protein Interactions of Membrane Proteins In Vivo

A biochemical approach is described to identify in vivo protein-protein interactions (PPI) of membrane proteins. The method combines protein cross-linking, affinity purification and mass spectrometry, and is adaptable to almost any cell type or organism. With this approach, even the identification of transient PPIs becomes possible.

Membrane proteins are essential for cell viability and are therefore important therapeutic targets1-3. Since they function in complexes4, methods to ...

Synthesis of an Intein-mediated Artificial Protein Hydrogel

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of this hydrogel are two protein block-copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. A highly hydrophilic random coil is inserted into one of the block-copolymers for water retention. Mixing of the two protein block copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit with crosslinkers at either end that rapidly self-assembles into a hydrogel. This hydrogel is very stable under both acidic and basic conditions, at temperatures up to 50 &#176;C, and in organic solvents. The hydrogel rapidly reforms after shear-induced rupture. Incorporation of a &#34;docking station peptide&#34; into the hydrogel building block enables convenient incorporation of &#34;docking protein&#34;-tagged target proteins. The hydrogel is compatible with tissue culture growth media, supports the diffusion of 20 kDa molecules, and enables the immobilization of bioactive globular proteins. The application of the intein-mediated protein hydrogel as an organic-solvent-compatible biocatalyst was demonstrated by encapsulating the horseradish peroxidase enzyme and corroborating its activity.

We present the synthesis of a split-intein-mediated protein hydrogel. The building blocks of this hydrogel are two protein copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. Mixing of the two protein copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit that self-assembles into a hydrogel. This hydrogel is highly pH- and temperature-stable, compatible with organic solvents, and easily incorporates functional globular proteins.

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of ...

Characterization of Complex Systems Using the Design of Experiments Approach: Transient Protein Expression in Tobacco as a Case Study

Plants provide multiple benefits for the production of biopharmaceuticals including low costs, scalability, and safety. Transient expression offers the additional advantage of short development and production times, but expression levels can vary significantly between batches thus giving rise to regulatory concerns in the context of good manufacturing practice. We used a design of experiments (DoE) approach to determine the impact of major factors such as regulatory elements in the expression construct, plant growth and development parameters, and the incubation conditions during expression, on the variability of expression between batches. We tested plants expressing a model anti-HIV monoclonal antibody (2G12) and a fluorescent marker protein (DsRed). We discuss the rationale for selecting certain properties of the model and identify its potential limitations. The general approach can easily be transferred to other problems because the principles of the model are broadly applicable: knowledge-based parameter selection, complexity reduction by splitting the initial problem into smaller modules, software-guided setup of optimal experiment combinations and step-wise design augmentation. Therefore, the methodology is not only useful for characterizing protein expression in plants but also for the investigation of other complex systems lacking a mechanistic description. The predictive equations describing the interconnectivity between parameters can be used to establish mechanistic models for other complex systems.

We describe a design of experiments approach that can be used to determine and model the influence of transgene regulatory elements, plant growth and development parameters, and incubation conditions on the transient expression of monoclonal antibodies and reporter proteins in plants.

Plants provide multiple benefits for the production of biopharmaceuticals including low costs, scalability, and safety. Transient expression offers the ...

Expression, Isolation, and Purification of Soluble and Insoluble Biotinylated Proteins for Nerve Tissue Regeneration

Recombinant protein engineering has utilized Escherichia coli (E. coli) expression systems for nearly 4 decades, and today E. coli is still the most widely used host organism. The flexibility of the system allows for the addition of moieties such as a biotin tag (for streptavidin interactions) and larger functional proteins like green fluorescent protein or cherry red protein. Also, the integration of unnatural amino acids like metal ion chelators, uniquely reactive functional groups, spectroscopic probes, and molecules imparting post-translational modifications has enabled better manipulation of protein properties and functionalities. As a result this technique creates customizable fusion proteins that offer significant utility for various fields of research. More specifically, the biotinylatable protein sequence has been incorporated into many target proteins because of the high affinity interaction between biotin with avidin and streptavidin. This addition has aided in enhancing detection and purification of tagged proteins as well as opening the way for secondary applications such as cell sorting. Thus, biotin-labeled molecules show an increasing and widespread influence in bioindustrial and biomedical fields. For the purpose of our research we have engineered recombinant biotinylated fusion proteins containing nerve growth factor (NGF) and semaphorin3A (Sema3A) functional regions. We have reported previously how these biotinylated fusion proteins, along with other active protein sequences, can be tethered to biomaterials for tissue engineering and regenerative purposes. This protocol outlines the basics of engineering biotinylatable proteins at the milligram scale, utilizing&#160; a T7 lac inducible vector and E. coli expression hosts, starting from transformation to scale-up and purification.

Developing biotinylatable fusion proteins has many potential applications in various fields of research. Recombinant protein engineering is a straight forward procedure that is cost-effective, providing high yields of custom-designed proteins.

Recombinant protein engineering has utilized Escherichia coli (E. coli) expression systems for nearly 4 decades, and today E. coli is still the most ...

Luminescence Resonance Energy Transfer to Study Conformational Changes in Membrane Proteins Expressed in Mammalian Cells

Luminescence Resonance Energy Transfer, or LRET, is a powerful technique used to measure distances between two sites in proteins within the distance range of 10-100 &#197;. By measuring the distances under various ligated conditions, conformational changes of the protein can be easily assessed. With LRET, a lanthanide, most often chelated terbium, is used as the donor fluorophore, affording advantages such as a longer donor-only emission lifetime, the flexibility to use multiple acceptor fluorophores, and the opportunity to detect sensitized acceptor emission as an easy way to measure energy transfer without the risk of also detecting donor-only signal. Here, we describe a method to use LRET on membrane proteins expressed and assayed on the surface of intact mammalian cells. We introduce a protease cleavage site between the LRET fluorophore pair. After obtaining the original LRET signal, cleavage at that site removes the specific LRET signal from the protein of interest allowing us to quantitatively subtract the background signal that remains after cleavage. This method allows for more physiologically relevant measurements to be made without the need for purification of protein.

We describe here an improved Luminescence Resonance Energy Transfer (LRET) method where we introduce a protease cleavage site between the donor and acceptor fluorophore sites. This modification allows us to obtain specific LRET signals arising from membrane proteins of interest, allowing for the study of membrane proteins without protein purification.

Luminescence Resonance Energy Transfer, or LRET, is a powerful technique used to measure distances between two sites in proteins within the distance range ...

Production, Characterization and Potential Uses of a 3D Tissue-engineered Human Esophageal Mucosal Model

The incidence of both esophageal adenocarcinoma and its precursor, Barrett&#8217;s Metaplasia, are rising rapidly in the western world. Furthermore esophageal adenocarcinoma generally has a poor prognosis, with little improvement in survival rates in recent years. These are difficult conditions to study and there has been a lack of suitable experimental platforms to investigate disorders of the esophageal mucosa.
A model of the human esophageal mucosa has been developed in the MacNeil laboratory which, unlike conventional 2D cell culture systems, recapitulates the cell-cell and cell-matrix interactions present in vivo and produces a mature, stratified epithelium similar to that of the normal human esophagus. Briefly, the model utilizes non-transformed normal primary human esophageal fibroblasts and epithelial cells grown within a porcine-derived acellular esophageal scaffold. Immunohistochemical characterization of this model by CK4, CK14, Ki67 and involucrin staining demonstrates appropriate recapitulation of the histology of the normal human esophageal mucosa.
This model provides a robust, biologically relevant experimental model of the human esophageal mucosa. It can easily be manipulated to investigate a number of research questions including the effectiveness of pharmacological agents and the impact of exposure to environmental factors such as alcohol, toxins, high temperature or gastro-esophageal refluxate components. The model also facilitates extended culture periods not achievable with conventional 2D cell culture, enabling, inter alia, the study of the impact of repeated exposure of a mature epithelium to the agent of interest for up to 20 days. Furthermore, a variety of cell lines, such as those derived from esophageal tumors or Barrett&#8217;s Metaplasia, can be incorporated into the model to investigate processes such as tumor invasion and drug responsiveness in a more biologically relevant environment.

This manuscript describes the production, characterization and potential uses of a tissue engineered 3D esophageal construct prepared from normal primary human esophageal fibroblast and squamous epithelial cells seeded within a de-cellularized porcine scaffold. The results demonstrate the formation of a mature stratified epithelium similar to the normal human esophagus.

The incidence of both esophageal adenocarcinoma and its precursor, Barrett&#8217;s Metaplasia, are rising rapidly in the western world. Furthermore ...

Biomechanical Characterization of Human Soft Tissues Using Indentation and Tensile Testing

Regenerative medicine aims to engineer materials to replace or restore damaged or diseased organs. The mechanical properties of such materials should mimic the human tissues they are aiming to replace; to provide the required anatomical shape, the materials must be able to sustain the mechanical forces they will experience when implanted at the defect site. Although the mechanical properties of tissue-engineered scaffolds are of great importance, many human tissues that undergo restoration with engineered materials have not been fully biomechanically characterized. Several compressive and tensile protocols are reported for evaluating materials, but with large variability it is difficult to compare results between studies. Further complicating the studies is the often destructive nature of mechanical testing. Whilst an understanding of tissue failure is important, it is also important to have knowledge of the elastic and viscoelastic properties under more physiological loading conditions.
This report aims to provide a minimally destructive protocol to evaluate the compressive and tensile properties of human soft tissues. As examples of this technique, the tensile testing of skin and the compressive testing of cartilage are described. These protocols can also be directly applied to synthetic materials to ensure that the mechanical properties are similar to the native tissue. Protocols to assess the mechanical properties of human native tissue will allow a benchmark by which to create suitable tissue-engineered substitutes.

Tissue biomechanics is important for maintaining cell shape and function and for determining phenotype. This report demonstrates non-destructive mechanical protocols for characterizing elastic and viscoelastic properties of human soft tissues, which can be directly applied to tissue-engineered substrates to allow a close matching of engineered materials to native tissue.

Regenerative medicine aims to engineer materials to replace or restore damaged or diseased organs. The mechanical properties of such materials should ...

Fabrication and Characterization of Optical Tissue Phantoms Containing Macrostructure

The rapid development of new optical imaging techniques is dependent on the availability of low-cost, customizable, and easily reproducible standards. By replicating the imaging environment, costly animal experiments to validate a technique may be circumvented. Predicting and optimizing the performance of in vivo and ex vivo imaging techniques requires testing on samples that are optically similar to tissues of interest. Tissue-mimicking optical phantoms provide a standard for evaluation, characterization, or calibration of an optical system. Homogenous polymer optical tissue phantoms are widely used to mimic the optical properties of a specific tissue type within a narrow spectral range. Layered tissues, such as the epidermis and dermis, can be mimicked by simply stacking these homogenous slab phantoms. However, many in vivo imaging techniques are applied to more spatially complex tissue where three dimensional structures, such as blood vessels, airways, or tissue defects, can affect the performance of the imaging system. 
This protocol describes the fabrication of a tissue-mimicking phantom that incorporates three-dimensional structural complexity using material with optical properties of tissue. Look-up tables provide India ink and titanium dioxide recipes for optical absorption and scattering targets. Methods to characterize and tune the material optical properties are described. The phantom fabrication detailed in this article has an internal branching mock airway void; however, the technique can be broadly applied to other tissue or organ structures.

Optical tissue phantoms are essential tools for calibration and characterization of optical imaging systems and validation of theoretical models. This article details a method for phantom fabrication that includes replication of tissue optical properties and three-dimensional tissue structure.

The rapid development of new optical imaging techniques is dependent on the availability of low-cost, customizable, and easily reproducible standards. By ...