[Characterization of cbm2813 encoding the cytochrome P450 enzyme in the biosynthetic gene cluster of carbomycin]

Carbomycin, a 16-membered macrolide antibiotic produced in Streptomyces thermotolerans, comprises two components, carbomycin A (CA) and carbomycin B (CB). CB is converted into CA through epoxidation of the C12-C13 double bond. The gene cbm2813, located in the biosynthetic gene cluster of carbomycin, encodes a cytochrome P450 enzyme considered to catalyze this epoxidation. In this study, the functional and enzymatic properties of the cytochrome P450 enzyme Cbm2813 in the carbomycin biosynthesis gene cluster were characterized by in vivo gene inactivation and in vitro enzymatic reactions. We employed the CRISPR-Cas9 system to delete cbm2813 and obtained the mutant Δcbm2813. The fermentation products of the mutant contained CB but not CA. Complementation of Δcbm2813 restored CA production. Cbm2813 was successfully expressed in Escherichia coli and then purified. In vitro enzyme assays confirmed that Cbm2813 specifically recognized CB but not structurally similar 16-membered macrolide antibiotics, such as josamycin, midecamycin, and isovalerylspiramycin I. Cbm2813 exhibited the maximal activity at pH 5.5 and 36 ℃, with the catalytic efficiency k_cat/K_m of 4.39×10³ L/(mol·s). Molecular docking suggested that the C9 carbonyl group of CB coordinated with the heme iron in the active site of the enzyme, ensuring strict substrate specificity. This study expands the toolbox of characterized P450 enzymes and advances the understanding of carbomycin biosynthesis.