[Sterol transport proteins in yeast: a review]

Sterols are a class of cyclopentano-perhydrophenanthrene derivatives widely present in living organisms. Sterols are important components of cell membranes. In addition, they also have important physiological and pharmacological activities. With the development of synthetic biology and metabolic engineering technology, yeast cells are increasingly used for the heterologous synthesis of sterols in recent years. Nevertheless, since sterols are hydrophobic macromolecules, they tend to accumulate in the membrane fraction of yeast cells and consequently trigger cytotoxicity, which hampers the further improvement of sterols yield. Therefore, revealing the mechanism of sterol transport in yeast, especially understanding the working principle of sterol transporters, is vital for designing strategies to relieve the toxicity of sterol accumulation and increasing sterol yield in yeast cell factories. In yeast, sterols are mainly transported through protein-mediated non-vesicular transport mechanisms. This review summarizes five types of sterol transport-related proteins that have been reported in yeast, namely OSBP/ORPs family proteins, LAM family proteins, ABC transport family proteins, CAP superfamily proteins, and NPC-like sterol transport proteins. These transporters play important roles in intracellular sterol gradient distribution and homeostasis maintenance. In addition, we also review the current status of practical applications of sterol transport proteins in yeast cell factories.