Structure-function analyses of cytochrome P450revI involved in reveromycin A biosynthesis

Numerous cytochrome P450s are involved in secondary metabolite biosynthesis. The biosynthetic gene cluster for reveromycin A (RM-A) also includes a P450 gene, revI. To understand the roles of P450revI, we comprehensively characterized the enzyme. The revI gene disruptant (ΔrevI) resulted in accumulation of reveromycin T (RM-T), and revI gene complementation restored RM-A production, indicating that the physiological substrate of P450revI is RM-T. Indeed, the purified P450revI catalyzed the C18-hydroxylation of RM-T more efficiently than the other RM derivatives tested. Moreover, the 1.4-Å resolution co-crystal structure of P450revI with RM-T revealed that the substrate binds the enzyme with a folded compact conformation for C18-hydroxylation. To address the structure-enzyme activity relationship, site-directed mutagenesis was performed in P450revI. Arg190Ala and Arg81Ala mutations, which abolished salt bridge formation with C1 and C24 carboxyl groups of RM-T, respectively, resulted in significant loss of enzyme activity. Moreover, the accumulation of RM-T in ΔrevI mutants enabled us to characterize its biological activity. Our results show that RM-T had stronger anticancer activity and isoleucyl-tRNA synthetase inhibition than RM-A. However, RM-T showed much less anti-osteoclastic activity than RM-A, indicating that hemisuccinate moiety is important for the activity.