Supporting activities of cognate redox partners for sterol-metabolizing P450 enzymes in Mycobacterium neoaurum

Steroids with anti-inflammatory, anti-allergic, endocrine-regulating, and other pharmaceutical activities represent the second most widely used class of drugs worldwide, following antibiotics. Their industrial production primarily relies on Mycobacteria-mediated biotransformation of sterols into key intermediates, followed by chemical or enzymatic modifications. While the sterol metabolic pathways in Mycobacteria have been intensively studied, the identification and functional characterization of key enzymes, particularly cytochrome P450 enzymes (CYPs or P450s) and their cognate redox partners, remain incomplete. Here, we heterologously expressed 24 P450s, 10 ferredoxin reductases (FdRs), and 12 ferredoxins (Fdxs) from Mycobacterium neoaurum ZC-1 in Escherichia coli. In vitro biochemical experiments identified five P450 enzymes (CYP125A76, CYP125A77, CYP125A78, CYP142A12, and CYP124A1) capable of catalyzing sterol side-chain terminal oxidation. Screening 120 redox partner combinations revealed FdR4662/Fdx4443 as the optimal cognate redox partners for all five P450 enzymes. With this redox partner pair, CYP142A12 achieved a conversion ratio of 89% for 4-cholesten-3-one with NADH as the preferred cofactor. Structural analyses indicate that the electron-transfer efficiency is primarily governed by electrostatic complementarity around the Fe-S cluster, the redox-center distance between the Fe-S cluster and heme-iron, and the FAD-to-cluster distance within the FdR-Fdx complex. These findings highlight the critical role of redox partner selection in enhancing P450 catalytic efficiency and provide a solid foundation for engineering high-efficiency industrial strains to improve steroid biomanufacturing and reduce production costs.