Strategies of codon optimization for high-level heterologous protein expression in microbial expression systems

Codon optimization includes strategies in gene design engineering, which uses synonymous codon changes to improve levels of protein production. Codon usage bias indicates that specific codons are used more often from other synonymous codons by gene translation. In the past decade, a variety of codon optimization methods have been used to design genes for optimal expression, which requires selection from a vast number of possible DNA sequences. Specific species differences in codon usage often indicate primary causes that affect levels of protein expression. The use of synthetically designed genes provides means for researchers to exercise more control on heterologous protein expression. Current studies show that codon optimization can affect protein conformation and function and increase expression levels. Over the past several years, considerable achievement in speed and cost of gene synthesis has facilitated complete redesign of entire gene sequences, significantly improving likelihood of high-level protein expression. This methodology significantly affects economic feasibility of microbial-based biotechnological processes for instance, by increasing volumetric productivities of recombinant proteins or facilitating the redesign of new biosynthetic routes for production of metabolites. Expression of proteins in heterologous hosts has become a cornerstone of modern biotechnology. This review discusses various codon optimization approaches that lead to high levels of protein expression and also a clarification to current applications of this technology.