Using of transporter proteins to improve the uptake efficiency of hydrophobic compounds by Escherichia coli: a coordinated synthesis of START protein and P450scc system proteins to enhance cholesterol biotransformation.

Synthesis of steroid drugs is possible through biotechnological methods, however, the low efficiency of transporting steroid substrates across microbial membranes is the challenge in using microorganisms for their production. STARD1 and STARD3 proteins (members of the START domain family) work in some mammalian cells in conjunction with the steroidogenic P450scc enzyme system (cytochrome P450scc, adrenodoxin reductase, and adrenodoxin), transporting cholesterol to the mitochondria, where cytochrome P450scc converts it into pregnenolone. In this study, we investigated the effect of STARD1 and STARD3 on P450scc efficiency in E. coli expression models. The combination of the STARD3(216-444) or STARD1(53-285) protein bearing an N-terminal periplasm-targeting sequence, with the P450scc system reconstituted in E. coli, resulted in an increase of pregnenolone synthesis by 3.2- and 1.9-fold, respectively, on a laboratory scale. STARD3(216-444) showed higher levels of expression and a greater effect on the incorporation of sterols into cells and whole-cell biotransformation of cholesterol, compared to STARD1(53-285). This study proposes a fundamentally new approach to optimizing the functioning of the P450scc system in microbial cells, which uses the cholesterol transfer protein to increase the uptake efficiency of a poorly soluble steroid substrate by bacteria. The demand for steroid medications is increasing, and the use of specific carrier proteins could be a useful tool to enhance the efficiency of whole-cell biosynthesis of various steroid compounds.