N-7′ methylation in apramycin: its biosynthesis and biological role

Apramycin, an aminoglycoside antibiotic widely used in veterinary medicine, contains a methyl group at N-7 ' of the unusual octose moiety. Here we report a detailed investigation of the enzyme responsible for N-7 ' methylation and the biological role of the methyl group in apramycin through a series of genetic and biochemical studies. We show that N-7 ' methylation is catalyzed by a putative N-methyltransferase AprI, and occurs following the AprP-catalyzed N-7 ' deacetylation step. Bioassay experiments indicate that N-7 '-demethyl-apramycin exhibits lower antibacterial activity than apramycin, suggesting the bioactivity-improving effect of the methyl group. Intriguingly, the target binding assay shows that apramycin and N-7 '-demethyl-apramycin exhibit the same level of affinity for the E. coli 16S rRNA, implying that apramycin may have an alternative target site in addition to the well-recognized 16S rRNA A-site. Therefore, this study provides insight into the assembly logic of apramycin at the pseudotrisaccharide stage and the development of apramycin derivatives with improved antibacterial activity based on the N-7 ' methyl group.

Automated summary

This study investigates the role of the N-7' methyl group in apramycin and reveals its impact on the antibiotic's antibacterial activity. The results suggest that the methyl group improves the bioactivity of apramycin, and that apramycin may have alternative target sites beyond the recognized 16S rRNA A-site.