A strategy for successful dual‐species protein expression of genes with non‐optimal codon usage destined for bacterial and yeast cell factories

Recombinant protein expression on an industrial scale traditionally utilizes one of two microbial workhorses: Escherichia coli or Saccharomyces cerevisiae. Additionally, random protein engineering of enzymes and proteins aimed for expression in S. cerevisiae are often mutagenized and pre-screened in E. coli before expression in yeast. This introduces artificial bottlenecks as the bacterial expression vector needs to be substituted for a yeast expression vector via sub-cloning, and the new library re-evaluated before a final screening in yeast. Here, we put forward a protein expression and engineering strategy that involves the use of a dual-host shuttle vector (pYB-Dual) designed with both a strong inducible yeast promoter (pGAL1), and a strong inducible bacterial promoter (pT7-RNAP), which allows for inducible protein expression in both species. Additionally, we demonstrate that by transforming the pYB-Dual vector into the E. coli strain Rosetta 2, which has elevated levels of 7 rare tRNAs, we can achieve high-level protein expression in both yeast and bacteria, even when using a mNeonGreen gene codon optimized for yeast. This dual expression vector is expected to remove bottlenecks during protein engineering of commercially important enzymes destined for high-titer expression in yeast.