Optimizing protein expression in the One-Pot PURE system: insights into reaction composition and translation efficiency

Abstract

The One-Pot PURE (Protein synthesis Using Recombinant Elements) system simplifies the preparation of traditional PURE systems by co-culturing and purifying 36 essential proteins for gene expression in a single step, thereby improving accessibility and affordability for widespread laboratory adoption and customization. However, replicating this protocol to match the productivity of traditional PURE systems can take considerable time and effort due to uncharacterized variability in the systems biochemical composition. In this work, we observed unstable PURE protein expression in E. coli strains M15/pREP4 and BL21(DE3) and addressed this using glucose-mediated catabolite repression to minimize burdensome background expression. We also identified differences in optimal protein induction timing between these two strains, leading to growth incompatibility in co-culture, and observed proteolysis of PURE proteins expressed in M15/pREP4. We showed that consolidating all expression vectors into a protease-deficient BL21(DE3) strain could minimize proteolysis. This single-strain system also led to more uniform cell growth at the time of protein induction, improving the stoichiometry of critical translation initiation factors in the PURE reaction for efficient protein production. In addition to optimizing One-Pot PURE protein composition, we found that variations in commercial energy solution formulations could compensate for suboptimal PURE protein stoichiometry. Moreover, our study revealed significant differences in the expression capacity of commercially available E. coli tRNAs, suggesting the potential of optimizing tRNA codons to improve protein translation. Taken together, this work highlights the complex biochemical interplay influencing protein expression capacity in the One-Pot PURE system and presents strategies to improve its robustness and productivity.