Gentamicin B (GB), a valuable starting material for the preparation of the semisynthetic aminoglycoside antibiotic isepamicin, is produced in trace amounts by the wild-type Micromonospora echinospora. Though the biosynthetic pathway to GB has remained obscure for decades, we have now identified three hidden pathways to GB production via seven hitherto unknown intermediates in M. echinospora. The narrow substrate specificity of a key glycosyltransferase and the C6′-amination enzymes, in combination with the weak and unsynchronized gene expression of the 2′-deamination enzymes, limits GB production in M. echinospora. The crystal structure of the aminotransferase involved in C6′-amination explains its substrate specificity. Some of the new intermediates displayed similar premature termination codon readthrough activity but with reduced toxicity compared to the natural aminoglycoside G418. This work not only led to the discovery of unknown biosynthetic routes to GB, but also demonstrated the potential to mine new aminoglycosides from nature for drug discovery.
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation of Korea grant (2016R1A2A1A05005078; (Y.J.Y.) funded by the Ministry of Science and ICT, Cooperative Research Program for Agriculture Science & Technology Development (PJ01316001; M.C.S.) and (PJ013179; J.W.P.) was funded by Rural Development Administration, under the project titled “Development of biomedical materials based on marine proteins” funded by the Ministry of Oceans and Fisheries (S.-S.C.), Republic of Korea, and the National Institutes of Health (GM035906) and the Welch Foundation (F-1511), USA (H.-w.L.)
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