Tunicamycins from Marine-Derived Streptomyces bacillaris Inhibit MurNAc-Pentapeptide Translocase in Staphylococcus aureus .

Four tunicamycin class compounds, tunicamycin VII ( 1 ), tunicamycin VIII ( 2 ), corynetoxin U17a ( 3 ), and tunicamycin IX ( 4 ), were isolated from the culture broth of the marine-derived actinomycete Streptomyces sp. MBTG32. The strain was identified using the 16S rDNA sequencing technique, and the isolated strain was closely related to Streptomyces bacillaris . The structures of the isolated compounds were elucidated based on spectroscopic data and comparisons with previously reported NMR data. Compounds 1 - 4 showed potent antibacterial activities against Gram-positive bacteria, especially Staphylococcus aureus, with MIC values of 0.13-0.25 µg/mL. Through a recombinant enzyme assay and overexpression analysis, we found that the isolated compounds exerted potent inhibitory effects on S. aureus MurNAc-pentapeptide translocase (MraY), with IC ₅₀ values of 0.08-0.21 µg/mL. The present results support that the underlying mechanism of action of tunicamycins isolated from marine-derived Streptomyces sp. is also associated with the inhibition of MraY enzyme activity in S. aureus .