Mechanism and engineering of endoplasmic reticulum-localized membrane protein folding in Saccharomyces cerevisiae

Correct folding of endoplasmic reticulum (ER)-localized membrane proteins, such as cytochrome P450, endows a synthetic biology host with crucial catalytic functions, which is of vital importance in the field of metabolic engineering and synthetic biology. However, due to complexed interaction with cellular membrane environment and other proteins (e.g., molecular chaperone) regulation, a substantial proportion of heterologous membrane proteins cannot be properly folded in the ER of Saccharomyces cerevisiae, a widely used synthetic biology host. In this review, we first introduce the four steps in membrane protein folding process and the affecting factors including the amino acid sequence of membrane protein, the folding process, molecular chaperones, quality control mechanism, and lipid environment in S. cerevisiae. Then, we summarize the metabolic engineering strategies to enhance the correct folding of ER-localized membrane proteins, such as by engineering and de novel design of membrane protein, regulation of the co-translational folding process, co-expression of molecular chaperones, modulation of ER quality, and lipids engineering. Finally, we discuss the limitations of current strategies and propose future research directions to address the key issues.