IGEM:IMPERIAL/2007/Projects/In-Veso/Implementation/Protocol1.3

1.3 Protocol for Adding Cell Extract into Vesicles

Day 1

Equipment

• Glass vial x1
• Gilsson pipette (200µl) + pipette tips
• Nitrogen tap
• 1000µl pipette tip
• Desiccator connected to a vacuum
• 25ml Glass pipette x1
• Sonicator with medium-sized probe
• 25°C incubator

Reagents

• 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) 20mg/ml in chloroform, ≥99.0%, or
• 1-Palmitoyl,2-oleoyl-sn-Glycero 3-phosphocholine (POPC) 20mg/ml in chloroform, ≥99.0%
• 10ml of dodecane

Preparing the lipid-oil suspension for the inner leaflet

1. Place 25 µl of the 20 mg/ml DOPC or POPC solution in a glass vial. (Equipment should generally be made of glass and not plastic so as to prevent adhesion of lipid molecules to plastic surface)
2. Using plastic tubing and a 1ml pipette tip, evaporate the chloroform under nitrogen to obtain a dry, thin lipid film. (Rubber tubes are not recommended as they are more likely to emit debris into the lipid film)
3. Put the vial in a desiccator connected to a vacuum for 1hr. (This is to remove the chloroform)
4. Add 10 ml of dodecane to reach a final lipid concentration of 0.05 mg/ml.
5. Place the vial containing the suspension in the ice bath.
6. Sonicate suspension for 30 min (Pulse 1, ~10 Amp). (This is to disperse the phospholipids)
7. Leave overnight at 25°C to ensure that the lipid molecules are fully dispersed in dodecane.

Day 2

Equipment

• Small tubes
• Aluminium foil
• 20µl pipette + tips
• 200µl pipette + tips
• 1000µl pipette + tips
• Tabletop centrifuge
• Vortex machine
• Syringe + stainless steel needle
• Glass slide + cover slip
• Optical microscope with phase contrast
• Fluorescent microscope

Reagents

• Commercial S30 E.coli extract
  • E.coli complete amino acid mixture
  • S30 premix without amino acid
  • S30 extract circular
  • Nuclease-free water
• Plasmid DNA wtih pTet-GFP construct

Preparation of Reaction

1. Add 5µl of E.coli complete amino acid mixture into a tube.
2. Then add 20µl of S30 premix without amino acid.
3. Next add 15µl of S30 extract circular.
4. Add an appropriate volume of plasmid DNA depending on DNA concentration.
5. Finally add nuclease-free water to bring final volume to 100µl.

Formation of mono-layer vesicles

1. Add 1µl of reaction into another tube containing 200μl of lipid-oil suspension.
2. Vortex gently for a few seconds. (This is to break up the small aqueous droplet to form an extract-oil emulsion)
3. Leave to stand for a few minutes. (Microdroplets will be stabilized by a monolayer of phospholipids at the oil–extract interface)

Formation of bi-layer vesicles

1. Place 50μl of the extract-oil emulsion on top of 25μl S30 premix with amino acids.
2. Leave to stand for a few minutes. (A monolayer of phospholipids will form at the interface of the biphasic solution)
3. Centrifuge at 120 x g for 10 min.

(Note: Alternatively, centrifuge at 30 x g for 20 min)

Collecting the vesicles:

1. Using a syringe with a stainless steel needle, collect some of the S30 premix.
2. Expel some of the premix to remove all air from the syringe and needle. (Expelling most of the S30 premix would ensure a less diluted solution of vesicles)
3. With the tip of the needle in the aqueous phase, gently expel the premix contained in the syringe. (This prevents the extraction of the lipid-oil suspension when the needle is plunged into the tube)
4. Gently recirculate the solution several times.
5. Aspirate most of the solution into the syringe, and remove the needle from the solution. (Be careful not to aspirate the lipid-oil suspension)
6. Wipe the tip of the needle clean.
7. Unload the vesicle suspension into a tube and store in the dark.
8. Use optical microscopy to check that the vesicles obtained were not deformed or aggregated. Ideally, the protocol should yield a few hundreds of vesicles and aggregates of 1 to a few tens of micrometers diameter. (Caution: Over-exposure of light under the microscope would bleach the GFP!!)

Notes

• Time required for Day 1: ~ 2h; for Day 2: ~2h.
• The protocol is based on A vesicle bioreactor as a step toward an artificial cell assembly by Vincent Noireaux and Albert Libchaber.
• Modifications to protocol:
  • The original protocol uses mineral oil instead of dodecane
  • The original protocol uses egg lecithin instead of DOPC or POPC
  • The original protocol does not use Span 80