This protocol describes the Cell-Free Protein Synthesis (CFPS) system used in constructing synthetic cells. It outlines key stages with representative results in different micro-compartments. The protocol aims to establish best practices for diverse laboratories in the synthetic cell community, advancing progress in synthetic cell development.
The Cell-Free Protein Synthesis (CFPS) system has been widely employed to facilitate the bottom-up assembly of synthetic cells. It serves as the host for the core machinery of the Central Dogma, standing as an optimal chassis for the integration and assembly of diverse artificial cellular mimicry systems. Despite its frequent use in the fabrication of synthetic cells, establishing a tailored and robust CFPS system for a specific application remains a nontrivial challenge. In this methods paper, we present a comprehensive protocol for the CFPS system, routinely employed in constructing synthetic cells. This protocol encompasses key stages in the preparation of the CFPS system, including the cell extract, template preparation, and routine expression optimization utilizing a fluorescent reporter protein. Additionally, we show representative results by encapsulating the CFPS system within various micro-compartments, such as monolayer droplets, double-emulsion vesicles, and chambers situated atop supported lipid bilayers. Finally, we elucidate the critical steps and conditions necessary for the successful assembly of these CFPS systems in distinct environments. We expect that our approach will facilitate the establishment of good working practices among various laboratories within the continuously expanding synthetic cell community, thereby accelerating progress in the field of synthetic cell development.
The synthesis of synthetic or artificial cells has emerged as a highly prominent field of interdisciplinary research, attracting substantial interest from scientists across the domains of synthetic biology, chemistry, and biophysics. These scientists are united by the common goal of constructing a minimal living cell1,2,3. The rapid growth of this field has been in step with significant advancements in critical technologies, such as recombinant DNA manipulation4, biomimetic materials5, and microfabrication techniques for compartmentalization6, including the Cell-Free Protein Synthesis (CFPS) method7. CFPS systems encompass the essential cellular machinery for transcription and translation, providing the foundational framework for the development and integration of multifunctional artificial cells.
Although CFPS techniques are frequently used in the assembly of synthetic cells, developing a robust and tailored CFPS system for the assembly of various synthetic cell systems remains a complex challenge. Currently, numerous CFPS systems are available, derived from both prokaryotes and eukaryotes model organisms8, each specialized for particular applications in synthetic cell synthesis. Beyond their central roles in transcription and translation, CFPS systems vary in their main components and associated preparation procedures. These variations, which include differences in cell extracts, RNA polymerases, template preparation methods, and buffer compositions, are largely due to the distinct development trajectories pursued by research groups that have intensively optimized their systems for maximal protein yield.
Among the various components of the CFPS system, the cell extract is a critical enzymatic pool for transcription and translation, and thus a key determinant of CFPS performance9. Escherichia coli (E. coli)–based CFPS is the most commonly utilized system due to its status as the best-understood prokaryotic organism. Furthermore, a fully reconstituted CFPS system comprising individually purified proteins and ribosomes, known as PURE10, has been developed by Ueda's research group, which is particularly suited for applications requiring a clear background. Today, even E. coli-based CFPS systems have diversified, especially in terms of the source strains for the extrac11 and methods of preparation12,13, RNA polymerase14,15, energy sources16,17, and buffer systems18,19. The most frequently used strains include K12 and B strain derivatives, such as A1920, JM10921, BL21 (DE3)22, and Rossetta223, alongside their genetically modified counterparts.
Initially, E. coli strains with reduced RNase and protease activities were chosen to enhance mRNA stability and the stability of newly synthesized recombinant proteins, leading to increased final protein yields24. Subsequently, E. coli extracts were engineered to facilitate specific post-translational modifications, including glycosylation25, phosphorylation26, and lipidation27, were developed to achieve the above posttranslational modifications. Additionally, an array of additives such as molecular chaperons28 and chemical stabilizers have been incorporated to aid the folding of target proteins, contributing to the diversification of CFPS systems. The bacteriophage T7 RNA polymerase, known for its high processivity, is predominantly employed for transcription, although other polymerases such as SP629 have also been utilized. E. coli endogenous RNA polymerase has been adapted for the prototyping of genetic circuits leveraging sigma factors30. Lastly, a variety of energy precursors31,32,33 and different salts and buffer components19,34,35 have been systematically optimized to enhance productivity.
Besides the CFPS system itself, the encapsulation methods as well as compartmentalization materials are also vital for the successful synthetic cell assembly. Various systems that have been developed to successfully encapsulate the CFPS reaction include surfactant-stabilized water/oil droplets, lipid/polymer, and their hybrid unilamellar vesicles (with diameters ranging from 50 nm to several μm), as well as planar-supported lipid bilayers. However, due to the complexed molecule content of the CFPS system, the success rate of encapsulation depends on specific cases, particularly for the formation of vesicles. To improve the success rate and efficiency of encapsulation of CFPS, various microfluid chips have been developed to facilitate the formation of both droplets and vesicles36. Nevertheless, additional chips and devices will need to be established.
This protocol delineates an E. coli CFPS system utilizing the BL21(DE3) strain, which is a commonly employed host for recombinant protein production. The protocol encompasses a detailed account of the cell extract preparation, template preparation, and standard expression optimization using a fluorescent reporter protein. Moreover, we present exemplary outcomes achieved by encapsulating the CFPS system within diverse micro-compartments, including monolayer droplets, double emulsion vesicles, and chambers situated atop supported lipid bilayers. Finally, we expound upon the pivotal procedural elements and the requisite conditions indispensable for the successful establishment of these CFPS systems within distinct environmental contexts.
This manuscript outlines a modified Cell-Free Protein Synthesis (CFPS) system designed for use in various micro-compartments across synthetic cell platforms, including water-in-oil droplets, GUVs, and SLBs. We utilized the standard E. coli recombinant protein expression host strain, BL21(DE3), as the source extract for constructing protein-centric synthetic cell systems. This approach yielded approximately 0.5 mg/mL of protein across different compartments. While other customized extract source strains could be …
The authors have nothing to disclose.
M. Y. acknowledges the funding from the Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (Grant No. KYCX22_2803). L.K. is thankful for the support of the Natural Science Research of Jiangsu Higher Education Institutions of China, China (Grant No. 17KJB180003), the Natural Science Foundation of Jiangsu Normal University, China (Grant No. 17XLR037), Priority Academic Program Development of Jiangsu Higher Education Institutions, China, and the Jiangsu Specially-Appointed Professor program, China.
1,2-dioleoyl-sn-glycero-3-phosphocholine(DOPC) | Avanti | 850375P | |
1,2-dioleoyl-sn-glycero-3-phospho-L-serine (sodium salt)(DOPS) | Avanti | 840035P | |
1,4 dithiothreitol (DTT) | Sigma-Aldrich | 1.11474 | |
1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) | Avanti | 850457P | |
3,5-cyclic AMP (cAMP) | Sigma-Aldrich | A9501 | |
50 mL tubes | Eppendorf | Eppendorf Tubes BioBased | |
50% hydrogen peroxide | Sigma-Aldrich | 516813 | |
Acetate | Sigma-Aldrich | A6283 | |
Agar powder | Sigma-Aldrich | 05040 | |
Alanin | Sigma-Aldrich | A4349 | |
Amicon Stirred Cells | MerckMillipore | UFSC05001 | |
Ammonium acetate (NH4OAc) | Sigma-Aldrich | A7262 | |
Arginin | Sigma-Aldrich | A4474 | |
Asparagin | Sigma-Aldrich | A0884 | |
Aspartat | Sigma-Aldrich | A5474 | |
ATP | Roche | 11140965001 | |
Atto 488 DOPE | Sigma-Aldrich | 67335 | |
Atto 647N DOPE | Sigma-Aldrich | 42247 | |
Baffled Erlenmeyer flask | Shuniu | 250 mL, 1000mL | |
Bovine Serum Albumin(BSA) | Roche | 10711454001 | |
Centrifugetube | Eppendorf | Eppendorf Tubes 3810X | |
Centrifugetube rack | Eppendorf | 0030119819 | |
Chemiluminescence and epifluorescence imaging system | Uvitec | Alliance Q9 Advanced | |
Chloroform | Sigma-Aldrich | 288306 | |
Confocal Laser Scanning Microscopy (LSM) | ZEISS | LSM 780 | |
Countess Cell Counting Chamber Slides | Thermo Fisher Scientific | C10283 | |
Coverslip | Thermo Scientific | Menzel BB02400500A113MNZ0 | |
creatine kinase (CK) | Roche | 10127566001 | |
Creatine phosphate (CP) | Sigma-Aldrich | 10621714001 | |
Culture dish | Huanqiu | 90 mm | |
Cystein | Sigma-Aldrich | C5360 | |
Cytidine 5'-triphosphate disodium salt (CTP) | aladdin | C101487 | |
Dialysis membrane | Spectrum | Standard RC Tubing MWCO: 12-14 kD | |
E.Z.N.A. Cycle Pure Kit | Omega Bio-Tek | D6492-01 | |
Electro-Heating Standing-Temperature Cultivator | Yiheng instrument | DHP-9602 | |
Ethylenediaminetetraacetic acid(EDTA) | Biosharp | 1100027 | |
Fluorescent plate reader | BioTek | Synergy 2 | |
Fluorinated oil | Suzhou CChip scientific instrument | 2%HFE7500 | |
Folinic acid | Sigma-Aldrich | 47612 | |
French Press | G.Heinemann | HTU-DIGI-Press | |
Glucose | Sigma-Aldrich | G7021 | |
Glutamat | Sigma-Aldrich | G5667 | |
Glutamin | Sigma-Aldrich | G5792 | |
Glycerol | Sigma-Aldrich | G5516 | |
Glycin | Sigma-Aldrich | G7126 | |
Guanosine 5'-triphosphate sodium salt hydrate(GTP) | Roche | 10106399001 | |
HEPES | Sigma-Aldrich | H3375 | |
HiPrep Q FF 16/10 | Cytiva | 28936543 | |
Histidin | Sigma-Aldrich | H6034 | |
Isoleucin | Sigma-Aldrich | I5281 | |
Isopropyl-β-D-thiogalactopyranoside (IPTG) | Sigma-Aldrich | I5502 | |
K2HPO4 | Sigma-Aldrich | P8281 | |
KH2PO4 | Sigma-Aldrich | P5655 | |
Leucin | Sigma-Aldrich | L6914 | |
Lysin | Sigma-Aldrich | L5501 | |
Magnesium acetate tetrahydrate (Mg(OAc)2 ) | Sigma-Aldrich | M5661 | |
Magnesium chloride(MgCl2) | Sigma-Aldrich | M2670 | |
Methionin | Sigma-Aldrich | M8439 | |
Microcentrifuge | Eppendorf | 5424 R | |
Mineral oil | Sigma-Aldrich | M5904 | |
Mini-PROTEAN Tetra Cell Systems | Bio-Rad | 1645050 | |
Multipurpose Centrifuge | Eppendorf | 5810 R | |
NaN3 | Sigma-Aldrich | S2002 | |
Nucleic Acid & Protein UV-Assay Measurements | IMPLEN | NanoPhotometer N60 | |
NucleoBond Xtra Maxi kit for transfection-grade plasmid DNA | MACHEREY-NAGEL | 740414.5 | |
Nunc-Immuno MicroWell 96 well polystyrene plates | Sigma-Aldrich | P8616 | |
PCR Thermal Cycler | Eppendorf | Mastercycler nexus | |
Peptone | Sigma-Aldrich | 83059 | |
Phenylalanin | Sigma-Aldrich | P8740 | |
Phosphoenolpyruvat (PEP) | GLPBIO | GC44635 | |
PMSF | Sigma-Aldrich | PMSF-RO | |
Polyethylene glycol 8000 (PEG 8000) | Sigma-Aldrich | 89510 | |
Potassium Acetate(KOAc) | Sigma-Aldrich | P5708 | |
Potassium chloride(KCl) | Sigma-Aldrich | P9541 | |
Potassium glutamate (K-glutamate) | Sigma-Aldrich | G1501 | |
Potassium hydroxide(KOH) | Sigma-Aldrich | 221473 | |
Prolin | Sigma-Aldrich | P8865 | |
Pyruvate kinase (PK) | Sigma-Aldrich | P9136 | |
Serin | Sigma-Aldrich | S4311 | |
Shaker | Zhichushakers | ZQZY-AF8 | |
Sodium chloride(NaCl) | Sigma-Aldrich | S5886 | |
Sodium hydroxide(NaOH) | Sigma-Aldrich | S5881 | |
Sucrose | aladdin | S112226 | |
Sulfuric acid | Sigma-Aldrich | 339741 | |
Syringe Filters | Jinteng | 0.45 μm | |
Test tube | Shuniu | 20 mL | |
TGX FastCast Acrylamide Kit, 12% | Bio-Rad | #1610175 | |
ThermoMixer | Eppendorf | ThermoMixer C | |
Threonin | Sigma-Aldrich | T8441 | |
Tris base | Sigma-Aldrich | V900483 | |
tRNA | Roche | 10109550001 | |
Tryptone | Sigma-Aldrich | T7293 | |
Tryptophan | Sigma-Aldrich | T8941 | |
Tyrosin | Sigma-Aldrich | T8566 | |
UTP Trisodium salt (UTP) | aladdin | U100365 | |
Vacuum Pump with Circulated Water System | Zhengzhou Greatwall Scientific Industrial and Trade Co.Ltd | SHB- | |
Valin | Sigma-Aldrich | V4638 | |
Vortex Mixers | Kylin-Bell | Vortex QL-861 | |
Water purification system | MerckMillipore | Direct ultrapure water (Type 1) | |
Yeast extract | Sigma-Aldrich | 70161 | |
β-mercaptoethanol | Sigma-Aldrich | 444203 |
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