Name: in vesiculo synthesis of peptide membrane precursors for autonomous vesicle growth
Uploaded: 2019-06-28T14:10:00
Description: Watch this Scientific Journal Video about In Vesiculo Synthesis of Peptide Membrane Precursors for Autonomous Vesicle Growth at JoVE.com

We gratefully acknowledge financial support through the DFG TRR 235 (Emergence of Life, project P15), the European Research Council (grant agreement no. 694410 AEDNA), and the TUM International Graduate School for Science and Engineering IGSSE (project no. 9.05). We thank E. Falgenhauer for her help with sample preparation. We thank A. Dupin and M. Schwarz-Schilling for their help with the TX-TL system and useful discussions. We thank N. B. Holland for useful discussions.

1. Expression of Elastin-like Polypeptides
<ol>
	<li>Day 1: Preparation of a starter culture and supplies for peptide expression
	<ol>
		<li>Prepare and autoclave expression culture flasks (4 x 2.5 L) and 3 L of LB medium. For 1 L of LB medium, add 25 g of LB powder to 1 L of ultrapure water.</li>
		<li>Prepare a starter culture with 100 mL of LB medium, 50 &#181;L of sterile-filtered (0.22 &#181;m filter) chloramphenicol solution (25 mg/mL in EtOH), and 50 &#181;L of sterile-filtered (0.22 &#181;m fil...

<ol>
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E., Chilkoti, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetically+encoded+synthesis+of+protein-based+polymers+with+precisely+specified+molecular+weight+and+sequence+by+recursive+directional+ligation:+examples+from+the+elastin-like+polypeptide+system.">Genetically encoded synthesis of protein-based polymers with precisely specified molecular weight and sequence by recursive directional ligation: examples from the elastin-like polypeptide system.</a> Biomacromolecules. 3 (2), 357-367 (2002).</li><li>Sun, Z. Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protocols+for+implementing+an+Escherichia+coli+based+TX-TL+cell-free+expression+system+for+synthetic+biology.">Protocols for implementing an Escherichia coli based TX-TL cell-free expression system for synthetic biology.</a> Journal of Visualized Experiments. (79), e50762 (2013).</li><li>Caschera, F., Noireaux, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+2.3+mg/ml+of+protein+with+an+all+Escherichia+coli+cell-free+transcription-translation+system.">Synthesis of 2.3 mg/ml of protein with an all Escherichia coli cell-free transcription-translation system.</a> Biochimie. 99, 162-168 (2014).</li><li>Schwarz-Schilling, M., Aufinger, L., M&#252;ckl, A., Simmel, F. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+communication+between+bacteria+and+cell-free+gene+expression+systems+within+linear+chains+of+emulsion+droplets.">Chemical communication between bacteria and cell-free gene expression systems within linear chains of emulsion droplets.</a> Integrative Biology. 8 (4), 564-570 (2016).</li><li>Garamella, J., Marshall, R., Rustad, M., Noireaux, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+All+E.+coli+TX-TL+Toolbox+2.0:+A+Platform+for+Cell-Free+Synthetic+Biology.">The All E. coli TX-TL Toolbox 2.0: A Platform for Cell-Free Synthetic Biology.</a> ACS Synthetic Biology. 5 (4), 344-355 (2016).</li><li>Rideau, E., Dimova, R., Schwille, P., Wurm, F. R., Landfester, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liposomes+and+polymersomes:+a+comparative+review+towards+cell+mimicking.">Liposomes and polymersomes: a comparative review towards cell mimicking.</a> Chemical Society Reviews. 47 (23), 8572-8610 (2018).</li><li>Filonov, G. S., Moon, J. D., Svensen, N., Broccoli Jaffrey, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Broccoli:+Rapid+Selection+of+an+RNA+Mimic+of+Green+Fluorescent+Protein+by+Fluorescence-Based+Selection+and+Directed+Evolution.">Broccoli: Rapid Selection of an RNA Mimic of Green Fluorescent Protein by Fluorescence-Based Selection and Directed Evolution.</a> Journal of the American Chemical Society. 136 (46), 16299-16308 (2014).</li><li>Zhang, S., Cahalan, M. 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Film rehydration is a common procedure for the creation of small unilamellar vesicles. The main source of failure is the wrong handling of the materials used in the procedure.

Initially, the ELPs are produced by E. coli cells. The yield after ELP purification can vary significantly depending on how carefully the protocol is conducted during its crucial steps. These are the inverse temperature cycling (ITC) step and th...

The creation of synthetic living cellular systems is usually approached from two different directions. In the top-down method, the genome of a bacterium is reduced to its essential components, ultimately leading to a minimal cell. In the bottom-up approach, artificial cells are assembled de novo from molecular components or cellular subsystems, which need to be functionally integrated into a consistent cell-like system.
In the de novo approach, compartmentalization of the necessary biochemical components is usually achieved using membranes made from phospholipids or fatty acids1,2,3,4. This is because &#34;modern&#34; cell membranes mainly consist of phospholipids, while fatty acids are regarded plausible candidates of prebiotic membrane enclosures5,6. For the formation of new membranes or to facilitate membrane growth, amphiphilic building blocks must be provided from the exterior7 or ideally through production within a membranous compartment using the corresponding anabolic processes4,8.
While lipid synthesis is a relatively complex metabolic process, peptides can be produced quite readily using cell-free gene expression reactions9,10. Hence, peptide membranes formed by amphiphilic peptides represent an interesting alternative to lipid membranes as enclosures for artificial cell mimics that are able to grow11.
Amphiphilic elastin-like di-block copolymers (ELPs) are an attractive class of peptides, which can serve as the building block for such membranes12. The basic amino acid sequence motif of ELPs is (GaGVP)n, where &#8220;a&#8221; can be any amino acid except for proline and &#8220;n&#8221; is the number of motif repeats13,14,15,16,17. ELPs have been created with a hydrophobic block containing mainly phenylalanine for a and a hydrophilic block mainly composed of glutamic acid11. Depending on a and solution parameters, such as pH and salt concentration, ELPs exhibit a so-called inverse temperature transition at temperature Tt, where the peptides undergo a fully reversible phase transition from a hydrophilic to hydrophobic state. The synthesis of the peptides can be easily implemented inside vesicles using the &#8220;TX-TL&#8221; bacterial cell extract11,18,19,20,21, which provides all necessary components for coupled transcription and translation reactions.
The TX-TL system was encapsulated together, with the DNA template encoding the ELPs into ELP vesicles utilizing dehydration-rehydration from glass beads as a solid support. The formation of vesicles occurs through rehydration of the dried peptides from the bead surface11. Other methods22 for vesicle formation can be used, which potentially show lower polydispersity and larger vesicle sizes (e.g., electro-formation, emulsion phase transfer, or microfluidics-based methods). To test the viability of the encapsulation method, transcription of the fluorogenic aptamer dBroccoli23 can alternatively be used11, which is less complex than gene expression with the TX-TL system.
Due to the expression of the membrane building blocks in vesiculo and their subsequent incorporation into the membrane, the vesicles start to grow11. Membrane incorporation of the ELPs can be demonstrated through a FRET assay. To this end, the ELPs used for formation of the initial vesicle population are be conjugated with fluorescent dyes in equal shares constituting a FRET pair. Upon expression of non-labeled ELPs in vesiculo and their incorporation into the membrane, the labeled ELPs in the membrane are diluted and consequently the FRET signal decreases11. As a versatile and common method for conjugation, copper catalyzed azide-alkyne cycloaddition is used. With the use of a stabilizing ligand such as tris(benzyltriazolylmethyl)-amine, the reaction can be carried out in an aqueous solution at a physiological pH without the hydrolysis of reactants11, which is appropriate for conjugation reactions involving peptides.
The following protocol presents a detailed description of the preparation for growing ELP-based peptidosomes. The expression of the peptides and vesicle formation using the glass beads method are described. Furthermore, it is described how to implement transcription of the fluorogenic dBroccoli aptamer and the transcription-translation reaction for protein expression inside the ELP vesicles. Finally, provided is a procedure for the conjugation of ELPs with fluorophores, which can be used to prove vesicle growth through a FRET assay11.

<table>
	<tbody>
		<tr>
			<td>2xYT</td>
			<td>MP biomedicals</td>
			<td>3012-032</td>
			<td></td>
		</tr>
		<tr>
			<td>3-PGA</td>
			<td>Sigma-Aldrich</td>
			<td>P8877</td>
			<td></td>
		</tr>
		<tr>
			<td>5PRIME Phase Lock GelTM tube</td>
			<td>VWR</td>
			<td>733-2478</td>
			<td></td>
		</tr>
		<tr>
			<td>alkine-conjugated Cy3</td>
			<td>Sigma-Aldrich</td>
			<td>777331</td>
			<td></td>
		</tr>
		<tr>
			<td>alkine-conjugated Cy5</td>
			<td>Sigma-Aldrich</td>
			<td>777358</td>
			<td></td>
		</tr>
		<tr>
			<td>ATP</td>
			<td>Sigma-Aldrich</td>
			<td>A8937</td>
			<td></td>
		</tr>
		<tr>
			<td>benzamidin</td>
			<td>Carl Roth</td>
			<td>CN38.2</td>
			<td></td>
		</tr>
		<tr>
			<td>BL21 Rosetta 2 E. coli strain</td>
			<td>Novagen</td>
			<td>71402</td>
			<td></td>
		</tr>
		<tr>
			<td>Bradford BSA Protein Assay Kit</td>
			<td>Bio-rad</td>
			<td>500-0201</td>
			<td></td>
		</tr>
		<tr>
			<td>cAMP</td>
			<td>Sigma-Aldrich</td>
			<td>A9501</td>
			<td></td>
		</tr>
		<tr>
			<td>carbenicillin</td>
			<td>Carl Roth</td>
			<td>6344.2</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloramphenicol</td>
			<td>Sigma-Aldrich</td>
			<td>C1919</td>
			<td></td>
		</tr>
		<tr>
			<td>chloramphenicol</td>
			<td>Carl Roth</td>
			<td>3886.3</td>
			<td></td>
		</tr>
		<tr>
			<td>chloroform</td>
			<td>Carl Roth</td>
			<td>4432.1</td>
			<td></td>
		</tr>
		<tr>
			<td>CoA</td>
			<td>Sigma-Aldrich</td>
			<td>C4282</td>
			<td></td>
		</tr>
		<tr>
			<td>CTP</td>
			<td>USB</td>
			<td>14121</td>
			<td></td>
		</tr>
		<tr>
			<td>CuSO4</td>
			<td>Carl Roth</td>
			<td>P024.1</td>
			<td></td>
		</tr>
		<tr>
			<td>DFHBI</td>
			<td>Lucerna Technologies</td>
			<td>410</td>
			<td></td>
		</tr>
		<tr>
			<td>DMSO</td>
			<td>Carl Roth</td>
			<td>A994.1</td>
			<td></td>
		</tr>
		<tr>
			<td>DNase I</td>
			<td>NEB</td>
			<td>M0303S</td>
			<td></td>
		</tr>
		<tr>
			<td>DTT</td>
			<td>Sigma-Aldrich</td>
			<td>D0632</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Carl Roth</td>
			<td>9065.2</td>
			<td></td>
		</tr>
		<tr>
			<td>Folinic acid</td>
			<td>Sigma-Aldrich</td>
			<td>F7878</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass beads, acid-washed</td>
			<td>Sigma-Aldrich</td>
			<td>G1277</td>
			<td></td>
		</tr>
		<tr>
			<td>GTP</td>
			<td>USB</td>
			<td>16800</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>H6147</td>
			<td></td>
		</tr>
		<tr>
			<td>IPTG (&#946;-isopropyl thiogalactoside )</td>
			<td>Sigma-Aldrich</td>
			<td>I6758</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Carl Roth</td>
			<td>P017.1</td>
			<td></td>
		</tr>
		<tr>
			<td>K-glutamate</td>
			<td>Sigma-Aldrich</td>
			<td>G1149</td>
			<td></td>
		</tr>
		<tr>
			<td>LB Broth</td>
			<td>Carl Roth</td>
			<td>X968.2</td>
			<td></td>
		</tr>
		<tr>
			<td>lysozyme</td>
			<td>Sigma-Aldrich</td>
			<td>L6876</td>
			<td></td>
		</tr>
		<tr>
			<td>methanol</td>
			<td>Carl Roth</td>
			<td>82.2</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Carl Roth</td>
			<td>KK36.3</td>
			<td></td>
		</tr>
		<tr>
			<td>Mg-glutamate</td>
			<td>Sigma-Aldrich</td>
			<td>49605</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro Bio-Spin Chromatography Columns</td>
			<td>Bio-Rad</td>
			<td>732-6204</td>
			<td></td>
		</tr>
		<tr>
			<td>NAD</td>
			<td>Sigma-Aldrich</td>
			<td>N6522</td>
			<td></td>
		</tr>
		<tr>
			<td>NHS-azide linker (y-azidobutyric acid oxysuccinimide ester)</td>
			<td>Baseclick</td>
			<td>BCL-033-5</td>
			<td></td>
		</tr>
		<tr>
			<td>PEG-8000</td>
			<td>Carl Roth</td>
			<td>263.2</td>
			<td></td>
		</tr>
		<tr>
			<td>pH stripes</td>
			<td>Carl Roth</td>
			<td>549.2</td>
			<td></td>
		</tr>
		<tr>
			<td>phenylmethylsulfonyl fluoride</td>
			<td>Carl Roth</td>
			<td>6367.2</td>
			<td></td>
		</tr>
		<tr>
			<td>phosphate-buffered saline</td>
			<td>VWR</td>
			<td>76180-684</td>
			<td></td>
		</tr>
		<tr>
			<td>phosphoric acid</td>
			<td>Sigma-Aldrich</td>
			<td>W290017</td>
			<td></td>
		</tr>
		<tr>
			<td>polyethyleneimine</td>
			<td>Sigma-Aldrich</td>
			<td>408727</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate dibasic solution</td>
			<td>Sigma-Aldrich</td>
			<td>P8584</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic solution</td>
			<td>Sigma-Aldrich</td>
			<td>P8709</td>
			<td></td>
		</tr>
		<tr>
			<td>Qiagen Miniprep Kit</td>
			<td>Qiagen</td>
			<td>27106</td>
			<td></td>
		</tr>
		<tr>
			<td>RNAPol reaction buffer</td>
			<td>NEB</td>
			<td>B9012</td>
			<td></td>
		</tr>
		<tr>
			<td>RNase inhibitor murine</td>
			<td>NEB</td>
			<td>M0314S</td>
			<td></td>
		</tr>
		<tr>
			<td>RNaseZap Wipes</td>
			<td>ThermoFisher</td>
			<td>AM9788</td>
			<td></td>
		</tr>
		<tr>
			<td>rNTP</td>
			<td>NEB</td>
			<td>N0466S</td>
			<td></td>
		</tr>
		<tr>
			<td>Roti-Phenol/Chloroform/Isoamyl alcohol</td>
			<td>Carlroth</td>
			<td>A156.1</td>
			<td></td>
		</tr>
		<tr>
			<td>RTS Amino Acid Sampler</td>
			<td>5 Prime</td>
			<td>2401530</td>
			<td></td>
		</tr>
		<tr>
			<td>Slide-A-Lyzer Dialysis Cassettes, 10k MWCO (Kit)</td>
			<td>Thermo-Scientific</td>
			<td>66382</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium chloride</td>
			<td>Carl Roth</td>
			<td>9265.1</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium hydroxide</td>
			<td>Carl Roth</td>
			<td>8655.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Spermidine</td>
			<td>Sigma-Aldrich</td>
			<td>85558</td>
			<td></td>
		</tr>
		<tr>
			<td>sterile-filtered (0.22 &#181;m filter)</td>
			<td>Carl Roth</td>
			<td>XH76.1</td>
			<td></td>
		</tr>
		<tr>
			<td>T7 polymerase</td>
			<td>NEB</td>
			<td>M0251S</td>
			<td></td>
		</tr>
		<tr>
			<td>TBTA (tris(benzyltriazolylmethyl)amine)</td>
			<td>Sigma-Aldrich</td>
			<td>678937</td>
			<td></td>
		</tr>
		<tr>
			<td>TCEP (tris(2-carboxyethyl)-phosphine hydrochloride)</td>
			<td>Sigma-Aldrich</td>
			<td>C4706</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris base</td>
			<td>Fischer</td>
			<td>BP1521</td>
			<td></td>
		</tr>
		<tr>
			<td>tRNA (from E. coli)</td>
			<td>Roche Applied Science</td>
			<td>MRE600</td>
			<td></td>
		</tr>
		<tr>
			<td>UTP</td>
			<td>USB</td>
			<td>23160</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vesiculo synthesis of peptide membrane precursors for autonomous vesicle growth

Compartmentalization of biochemical reactions is a central aspect of synthetic cells. For this purpose, peptide-based reaction compartments serve as an attractive alternative to liposomes or fatty acid-based vesicles. Externally or within the vesicles, peptides can be easily expressed and simplify the synthesis of membrane precursors. Provided here is a protocol for the creation of vesicles with diameters of ~200 nm based on the amphiphilic elastin-like polypeptides (ELP) utilizing dehydration-rehydration from glass beads. Also presented are protocols for bacterial ELP expression and purification via inverse temperature cycling, as well as their covalent functionalization with fluorescent dyes. Furthermore, this report describes a protocol to enable the transcription of RNA aptamer dBroccoli inside ELP vesicles as a less complex example for a biochemical reaction. Finally, a protocol is provided, which allows in vesiculo expression of fluorescent proteins and the membrane peptide, whereas synthesis of the latter results in vesicle growth.

Vesicle production 
Figure 1 shows transmission electron microscopy (TEM) images of vesicles prepared with different swelling solutions and the glass beads method (also see Vogele et al.11). For the sample in Figure 1A, only PBS was used as swelling solution to prove the formation of vesicles and to determine their size. When TX-TL was used as swelling solution (Figure 1B), the vesicles ...

Watch this Scientific Journal Video about In Vesiculo Synthesis of Peptide Membrane Precursors for Autonomous Vesicle Growth at JoVE.com

In Vesiculo Synthesis of Peptide Membrane Precursors for Autonomous Vesicle Growth

Presented here are protocols for the creation of peptide-based small unilamellar vesicles capable of growth. To facilitate in vesiculo production of the membrane peptide, these vesicles are equipped with a transcription-translation system and the peptide-encoding plasmid.

Compartmentalization of biochemical reactions is a central aspect of synthetic cells. For this purpose, peptide-based reaction compartments serve as an ...

In our protocol, we use film re-hydration from small glass beads to form reaction compartments made of peptides. In experiments, we benefit from the protocol's simplicity and robustness. The main advantage of this technique is the ability to incorporate even sensitive samples, such as the used crude cell extract.Contact with organic solvents will significantly affect the sample. To begin this procedure, use a centrifugal vacuum concentrator to concentrate the ELP solution to 1.1 millimolar. Mix 200 microliters of this concentrated solution with 1, 250 microliters of a two to one chloroform and methanol mixture.Vortex the solution to mix thoroughly. Next, add 1.5 grams of spherical glass beads to a ten milliliter round bottom flask. Add the ELP and chloroform methanol solution to the round bottom flask, and gently shake to mix.Connect the flask to a rotary evaporator. Adjust the speed to 150 RPM and regulate the pressure to 20, 000 pascals for approximately four minutes, until the liquid is evaporated at room temperature. It's important to be careful when using the rotary evaporator due to possible boiling retardation.After this, loosely wrap aluminum foil around the opening of the round bottom flask to prevent the loss of glass beads and place the flask into a desiccator for at least one hour, to ensure that the remaining chloroform and methanol are evaporated. For a single experiment, mix 100 milligrams of the peptide covered glass beads with 60 microliters of a swelling solution. Incubate this sample at 25 degrees Celsius for five minutes.Use a table top centrifuge to centrifuge the samples quickly and sediment the glass beads. Then use a pipette to collect the supernatant, which contains the vesicles. First, mix 100 microliters of the pre-purified plasmid DNA with 100 microliters of either Roti-Phenol, chloroform, or isoamyl alcohol in a micro centrifuge tube to enable better phase separation.Gently invert the tube up to six times and centrifuge at 16, 000 times g and room temperature for five minutes. Then, add 200 microliters of chloroform to the upper phase, and invert the tube up to six times. Centrifuge the sample at 16, 000 times g and room temperature for five minutes.After this, pipette the supernatant to a separate tube and add 10 microliters of three molar sodium acetate for ethanol precipitation. Add one milliliter of cold ethanol at 80 degrees Celsius and store the sample at 80 degrees Celsius for one hour. Next, centrifuge the sample at 16, 000 times g and four degrees Celsius for 15 minutes.Decant the supernatant and add one milliliter of cold 70%ethanol at 20 degrees Celsius. Centrifuge at 16, 000 times g and four degrees Celsius for five minutes. Then, remove the liquid by pipetting, being careful to not disturb the DNA pellet.Store the sample at room temperature for approximately 15 minutes to evaporate the remaining ethanol. After this, add ultra pure water to the sample to adjust the sample concentration to approximately 300 nanomolar, which is measured by absorption at 260 nanometers. To prepare the transcription-translation reaction, follow the prepared crude cell extraction and the reaction buffer on ice.For a 60 microliter reaction mix, add the plasma DNA to 37.5 microliters of the reaction buffer, add 28.7 microliters of crude cell extract and fill with ultra pure water to a final volume of 58.8 microliters. Right before the reaction starts, add 1.2 microliters of the T7RNA polymerase solution, and pipette up and down to mix. Incubate the sample and a swelling solution at 29 degrees Celsius for the duration of the experiment, which is typically four to eight hours.Transmission electron microscopy images of vesicles show that various swelling solutions, such as TX/TL or even only PBS can be used to form vesicles. For both solutions, size determination is a straight forward step. Dynamic light scattering shows that vesicles prepared without the glass beads method result in a diameter of 134 nanometers, with a polydispersity of 25%When glass beads are used, the diameter results in 168 nanometers, with a polydispersity of 21%The fluorescence intensity of two fluorescent proteins, which are expressed inside the ELP vesicles, are then measured using a fluorescence plate reader.It is important to note that after vesicle formation, the contents of the vesicles and the outer solution are the same, thus, the antibiotic Kanamycin is added to the exterior solution to suppress protein expression. As a control, Kanamycin is also added to the swelling solution, in which case protein expression inside of the vesicle is suppressed. This indicates that Kanamycin does not diffuse through the membrane, and suppresses internal expression constantly, all the time.The FRET assay is then performed to demonstrate ELP incorporation into the membrane. Upon expression of the membrane ELPs, additional peptides incorporate into the membrane, which increases the average distance between the FRET pairs, and which results in an increase of donor signal. The presented technique can be used to produce simple reaction containers or to create artificial cells with peptide-based membranes.The content inside can be chosen as needed. By using these peptide vesicles, we can now look forward on more complex synthesis reactions within them.

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Research

JoVE Journal

Bioengineering

Axon Stretch Growth: The Mechanotransduction of Neuronal Growth

During pre-synaptic embryonic development, neuronal processes traverse short distances to reach their targets via growth cone. Over time, neuronal somata are separated from their axon terminals due to skeletal growth of the enlarging organism (Weiss 1941; Gray, Hukkanen et al. 1992). This mechanotransduction induces a secondary mode of neuronal growth capable of accommodating continual elongation of the axon (Bray 1984; Heidemann and Buxbaum 1994; Heidemann, Lamoureux et al. 1995; Pfister, Iwata et al. 2004).
Axon Stretch Growth (ASG) is conceivably a central factor in the maturation of short embryonic processes into the long nerves and white matter tracts characteristic of the adult nervous system. To study ASG in vitro, we engineered bioreactors to apply tension to the short axonal processes of neuronal cultures (Loverde, Ozoka et al. 2011). Here, we detail the methods we use to prepare bioreactors and conduct ASG. First, within each stretching lane of the bioreactor, neurons are plated upon a micro-manipulated towing substrate. Next, neurons regenerate their axonal processes, via growth cone extension, onto a stationary substrate. Finally, stretch growth is performed by towing the plated cell bodies away from the axon terminals adhered to the stationary substrate; recapitulating skeletal growth after growth cone extension.
Previous work has shown that ASG of embryonic rat dorsal root ganglia neurons are capable of unprecedented growth rates up to 10mm/day, reaching lengths of up to 10cm; while concurrently resulting in increased axonal diameters (Smith, Wolf et al. 2001; Pfister, Iwata et al. 2004; Pfister, Bonislawski et al. 2006; Pfister, Iwata et al. 2006; Smith 2009). This is in dramatic contrast to regenerative growth cone extension (in absence of mechanical stimuli) where growth rates average 1mm/day with successful regeneration limited to lengths of less than 3cm (Fu and Gordon 1997; Pfister, Gordon et al. 2011). Accordingly, further study of ASG may help to reveal dysregulated growth mechanisms that limit regeneration in the absence of mechanical stimuli.

A unique tissue engineering method was developed to elongate numerous nerve fibers in culture by recapitulating axon stretch growth; a form of nervous system growth whereby nerves elongate in conjunction with growth of the enlarging body.

During pre-synaptic embryonic development, neuronal processes traverse short distances to reach their targets via growth cone. Over time, neuronal somata ...

Gold Nanostar Synthesis with a Silver Seed Mediated Growth Method

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape 1-5. There is a great interest in using nano-colloids for photo-thermal ablation, drug delivery and many other biomedical applications 6. Gold is particularly used because of its low toxicity 7-9. A property of metal nano-colloids is that they can have a strong surface plasmon resonance 10. The peak of the surface plasmon resonance mode depends on the structure and composition of the metal nano-colloids. Since the surface plasmon resonance mode is stimulated with light there is a need to have the peak absorbance in the near infrared where biological tissue transmissivity is maximal 11, 12.
We present a method to synthesize star shaped colloidal gold, also known as star shaped nanoparticles 13-15 or nanostars 16. This method is based on a solution containing silver seeds that are used as the nucleating agent for anisotropic growth of gold colloids 17-22. Scanning electron microscopy (SEM) analysis of the resulting gold colloid showed that 70 % of the nanostructures were nanostars. The other 30 % of the particles were amorphous clusters of decahedra and rhomboids. The absorbance peak of the nanostars was detected to be in the near infrared (840 nm). Thus, our method produces gold nanostars suitable for biomedical applications, particularly for photo-thermal ablation.

We synthesized star shaped gold nanostars using a silver seed mediated growth method. The diameter of the nanostars ranges from 200 to 300 nm and the number of tips vary from 7 to 10. The nanoparticles have a broad surface plasmon resonance mode centered in the near infrared.

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape 1-5. There is a great interest ...

Cultivation of Human Neural Progenitor Cells in a 3-dimensional Self-assembling Peptide Hydrogel

The influence of 3-dimensional (3D) scaffolds on growth, proliferation and finally neuronal differentiation is of great interest in order to find new methods for cell-based and standardised therapies in neurological disorders or neurodegenerative diseases. 3D structures are expected to provide an environment much closer to the in vivo situation than 2D cultures. In the context of regenerative medicine, the combination of biomaterial scaffolds with neural stem and progenitor cells holds great promise as a therapeutic tool.1-5 Culture systems emulating a three dimensional environment have been shown to influence proliferation and differentiation in different types of stem and progenitor cells. Herein, the formation and functionalisation of the 3D-microenviroment is important to determine the survival and fate of the embedded cells.6-8 Here we used PuraMatrix9,10 (RADA16, PM), a peptide based hydrogel scaffold, which is well described and used to study the influence of a 3D-environment on different cell types.7,11-14 PuraMatrix can be customised easily and the synthetic fabrication of the nano-fibers provides a 3D-culture system of high reliability, which is in addition xeno-free.
Recently we have studied the influence of the PM-concentration on the formation of the scaffold.13 In this study the used concentrations of PM had a direct impact on the formation of the 3D-structure, which was demonstrated by atomic force microscopy. A subsequent analysis of the survival and differentiation of the hNPCs revealed an influence of the used concentrations of PM on the fate of the embedded cells. However, the analysis of survival or neuronal differentiation by means of immunofluorescence techniques posses some hurdles. To gain reliable data, one has to determine the total number of cells within a matrix to obtain the relative number of e.g. neuronal cells marked by &beta;III-tubulin. This prerequisites a technique to analyse the scaffolds in all 3-dimensions by a confocal microscope or a comparable technique like fluorescence microscopes able to take z-stacks of the specimen. Furthermore this kind of analysis is extremely time consuming. 
Here we demonstrate a method to release cells from the 3D-scaffolds for the later analysis e.g. by flow cytometry. In this protocol human neural progenitor cells (hNPCs) of the ReNcell VM cell line (Millipore USA) were cultured and differentiated in 3D-scaffolds consisting of PuraMatrix (PM) or PuraMatrix supplemented with laminin (PML). In our hands a PM-concentration of 0.25% was optimal for the cultivation of the cells13, however the concentration might be adapted to other cell types.12 The released cells can be used for e.g. immunocytochemical studies and subsequently analysed by flow cytometry. This speeds up the analysis and more over, the obtained data rest upon a wider base, improving the reliability of the data.

Here we describe the use of a self-assembling 3-dimensional scaffold to culture human neural progenitor cells. We present a protocol to release the cells from the scaffolds to be analysed subsequently e.g. by flow cytometry. This protocol might be adapted to other cell types to perform detailed mechanistically studies.

The  influence of 3-dimensional (3D) scaffolds on growth, proliferation and finally  neuronal differentiation is of great interest in order to find new ...

Generation and Recovery of &beta;-cell Spheroids From Step-growth PEG-peptide Hydrogels

Hydrogels are hydrophilic crosslinked polymers that provide a three-dimensional microenvironment with tissue-like elasticity and high permeability for culturing therapeutically relevant cells or tissues. Hydrogels prepared from poly(ethylene glycol) (PEG) derivatives are increasingly used for a variety of tissue engineering applications, in part due to their tunable and cytocompatible properties. In this protocol, we utilized thiol-ene step-growth photopolymerizations to fabricate PEG-peptide hydrogels for encapsulating pancreatic MIN6 b-cells. The gels were formed by 4-arm PEG-norbornene (PEG4NB) macromer and a chymotrypsin-sensitive peptide crosslinker (CGGYC). The hydrophilic and non-fouling nature of PEG offers a cytocompatible microenvironment for cell survival and proliferation in 3D, while the use of chymotrypsin-sensitive peptide sequence (CGGY&darr;C, arrow indicates enzyme cleavage site, while terminal cysteine residues were added for thiol-ene crosslinking) permits rapid recovery of cell constructs forming within the hydrogel. The following protocol elaborates techniques for: (1) Encapsulation of MIN6 &beta;-cells in thiol-ene hydrogels; (2) Qualitative and quantitative cell viability assays to determine cell survival and proliferation; (3) Recovery of cell spheroids using chymotrypsin-mediated gel erosion; and (4) Structural and functional analysis of the recovered spheroids.

Generation and Recovery of &amp;#946;-cell Spheroids From Step-growth PEG-peptide Hydrogels

The following protocol provides techniques for encapsulating pancreatic &#x03B2;-cells in step-growth PEG-peptide hydrogels formed by thiol-ene photo-click reactions. This material platform not only offers a cytocompatible microenvironment for cell encapsulation, but also permits user-controlled rapid recovery of cell structures formed within the hydrogels.

Hydrogels are hydrophilic crosslinked polymers that provide a three-dimensional  microenvironment with tissue-like elasticity and high permeability for  ...

Lipid Bilayer Vesicle Generation Using Microfluidic Jetting

Bottom-up synthetic biology presents a novel approach for investigating and reconstituting biochemical systems and, potentially, minimal organisms. This emerging field engages engineers, chemists, biologists, and physicists to design and assemble basic biological components into complex, functioning systems from the bottom up. Such bottom-up systems could lead to the development of artificial cells for fundamental biological inquiries and innovative therapies1,2. Giant unilamellar vesicles (GUVs) can serve as a model platform for synthetic biology due to their cell-like membrane structure and size. Microfluidic jetting, or microjetting, is a technique that allows for the generation of GUVs with controlled size, membrane composition, transmembrane protein incorporation, and encapsulation3. The basic principle of this method is the use of multiple, high-frequency fluid pulses generated by a piezo-actuated inkjet device to deform a suspended lipid bilayer into a GUV. The process is akin to blowing soap bubbles from a soap film. By varying the composition of the jetted solution, the composition of the encompassing solution, and/or the components included in the bilayer, researchers can apply this technique to create customized vesicles. This paper describes the procedure to generate simple vesicles from a droplet interface bilayer by microjetting.

Microfluidic jetting against a droplet interface lipid bilayer provides a reliable way to generate vesicles with control over membrane asymmetry, incorporation of transmembrane proteins, and encapsulation of material. This technique can be applied to study a variety of biological systems where compartmentalized biomolecules are desired.

Bottom-up synthetic biology presents a novel approach for investigating and reconstituting biochemical systems and, potentially, minimal organisms. This ...

Analysis of Tubular Membrane Networks in Cardiac Myocytes from Atria and Ventricles

In cardiac myocytes a complex network of membrane tubules - the transverse-axial tubule system (TATS) - controls deep intracellular signaling functions. While the outer surface membrane and associated TATS membrane components appear to be continuous, there are substantial differences in lipid and protein content. In ventricular myocytes (VMs), certain TATS components are highly abundant contributing to rectilinear tubule networks and regular branching 3D architectures. It is thought that peripheral TATS components propagate action potentials from the cell surface to thousands of remote intracellular sarcoendoplasmic reticulum (SER) membrane contact domains, thereby activating intracellular Ca2+ release units (CRUs). In contrast to VMs, the organization and functional role of TATS membranes in atrial myocytes (AMs) is significantly different and much less understood. Taken together, quantitative structural characterization of TATS membrane networks in healthy and diseased myocytes is an essential prerequisite towards better understanding of functional plasticity and pathophysiological reorganization. Here, we present a strategic combination of protocols for direct quantitative analysis of TATS membrane networks in living VMs and AMs. For this, we accompany primary cell isolations of mouse VMs and/or AMs with critical quality control steps and direct membrane staining protocols for fluorescence imaging of TATS membranes. Using an optimized workflow for confocal or superresolution TATS image processing, binarized and skeletonized data are generated for quantitative analysis of the TATS network and its components. Unlike previously published indirect regional aggregate image analysis strategies, our protocols enable direct characterization of specific components and derive complex physiological properties of TATS membrane networks in living myocytes with high throughput and open access software tools. In summary, the combined protocol strategy can be readily applied for quantitative TATS network studies during physiological myocyte adaptation or disease changes, comparison of different cardiac or skeletal muscle cell types, phenotyping of transgenic models, and pharmacological or therapeutic interventions.

In cardiac myocytes, tubular membrane structures form intracellular networks. We describe optimized protocols for i) isolation of myocytes from mouse heart including quality control, ii) live cell staining for state-of-the-art fluorescence microscopy, and iii) direct image analysis to quantify the component complexity and the plasticity of intracellular membrane networks.

In cardiac myocytes a complex network of membrane tubules - the transverse-axial tubule system (TATS) - controls deep intracellular signaling functions. ...

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 ...

Polyelectrolyte Complex for Heparin Binding Domain Osteogenic Growth Factor Delivery

During reconstructive bone surgeries, supraphysiological amounts of growth factors are empirically loaded onto scaffolds to promote successful bone fusion. Large doses of highly potent biological agents are required due to growth factor instability as a result of rapid enzymatic degradation as well as carrier inefficiencies in localizing sufficient amounts of growth factor at implant sites. Hence, strategies that prolong the stability of growth factors such as BMP-2/NELL-1, and control their release could actually lower their efficacious dose and thus reduce the need for larger doses during future bone regeneration surgeries. This in turn will reduce side effects and growth factor costs. Self-assembled PECs have been fabricated to provide better control of BMP-2/NELL-1 delivery via heparin binding and further potentiate growth factor bioactivity by enhancing in vivo stability. Here we illustrate the simplicity of PEC fabrication which aids in the delivery of a variety of growth factors during reconstructive bone surgeries.

Self-assembled polyelectrolyte complexes (PEC) fabricated from heparin and protamine were deposited on alginate beads to entrap and regulate the release of osteogenic growth factors. This delivery strategy enables a 20-fold reduction of BMP-2 dose in spinal fusion applications. This article illustrates the benefits and fabrication of PECs.

During reconstructive bone surgeries, supraphysiological amounts of growth factors are empirically loaded onto scaffolds to promote successful bone ...

Synthesis of Monocyte-targeting Peptide Amphiphile Micelles for Imaging of Atherosclerosis

Atherosclerosis is a major contributor to cardiovascular disease, the leading cause of death worldwide, which claims 17.3 million lives annually. Atherosclerosis is also the leading cause of sudden death and myocardial infarction, instigated by unstable plaques that rupture and occlude the blood vessel without warning. Current imaging modalities cannot differentiate between stable and unstable plaques that rupture. Peptide amphiphiles micelles (PAMs) can overcome this drawback as they can be modified with a variety of targeting moieties that bind specifically to diseased tissue. Monocytes have been shown to be early markers of atherosclerosis, while large accumulation of monocytes is associated with plaques prone to rupture. Hence, nanoparticles that can target monocytes can be used to discriminate different stages of atherosclerosis. To that end, here, we describe a protocol for the preparation of monocyte-targeting PAMs (monocyte chemoattractant protein-1 (MCP-1) PAMs). MCP-1 PAMs are self-assembled through synthesis under mild conditions to form nanoparticles of 15 nm in diameter with near neutral surface charge. In vitro, PAMs were found to be biocompatible and had a high binding affinity for monocytes. The methods described herein show promise for a wide range of applications in atherosclerosis as well as other inflammatory diseases.

This paper presents a method involving the synthesis and characterization of monocyte-targeting peptide amphiphile micelles and the corresponding assays to test for biocompatibility and ability of the micelle to bind to monocytes.

Atherosclerosis is a major contributor to cardiovascular disease, the leading cause of death worldwide, which claims 17.3 million lives annually. ...

Visualization of Germinosomes and the Inner Membrane in Bacillus subtilis Spores

The small size of spores and the relatively low abundance of germination proteins, cause difficulties in their microscopic analyses using epifluorescence microscopy. Super-resolution three-dimensional Structured Illumination Microscopy (3D-SIM) is a promising tool to overcome this hurdle and reveal the molecular details of the process of germination of Bacillus subtilis (B. subtilis) spores. Here, we describe the use of a modified SIMcheck (ImageJ)-assistant 3D imaging process and fluorescent reporter proteins for SIM microscopy of B. subtilis spores&#8217; germinosomes, cluster(s) of germination proteins. We also present a (standard)3D-SIM imaging procedure for FM4-64 staining of B. subtilis spore membranes. By using these procedures, we obtained unsurpassed resolution for germinosome localization and show that &#62;80% of B. subtilis KGB80 dormant spores obtained after sporulation on defined minimal MOPS medium have one or two GerD-GFP and GerKB-mCherry foci. Bright foci were also observed in FM4-64 stained spores&#8217; 3D-SIM images suggesting that inner membrane lipid domains of different fluidity likely exist. Further studies that use double labeling procedures with membrane dyes and germinosome reporter proteins to assess co-localization and thus get an optimal overview of the organization of Bacillus germination proteins in the inner spore membrane are possible.

Visualization of Germinosomes and the Inner Membrane in Bacillus subtilis Spores

Germinant receptor proteins cluster in &#8216;germinosomes&#8217; in the inner membrane of Bacillus subtilis spores. We describe a protocol using super resolution microscopy and fluorescent reporter proteins to visualize germinosomes. The protocol also identifies spore inner membrane domains that are preferentially stained with the membrane dye FM4-64.

The small size of spores and the relatively low abundance of germination proteins, cause difficulties in their microscopic analyses using epifluorescence ...