Insights into Arsenic Secondary Metabolism in Actinomycetes from the Structure and Biosynthesis of Bisenarsan

The unique bioactivities of arsenic-containing secondarymetaboliteshave been revealed recently, but studies on arsenic secondary metabolismin microorganisms have been extremely limited. Here, we focused onthe organoarsenic metabolite with an unknown chemical structure, namedbisenarsan, produced by well-studied model actinomycetes and elucidatedits structure by combining feeding of the putative biosynthetic precursor(2-hydroxyethyl)arsonic acid to Streptomyces lividans 1326 and detailed NMR analyses. Bisenarsan is the first characterizedactinomycete-derived arsenic secondary metabolite and may functionas a prototoxin form of an antibacterial agent or be a detoxificationproduct of inorganic arsenic species. We also verified the previouslyproposed genes responsible for bisenarsan biosynthesis, especiallythe (2-hydroxyethyl)arsonic acid moiety. Notably, we suggest thata C-As bond in bisenarsan is formed by the intramolecular rearrangementof a pentavalent arsenic species (arsenoenolpyruvate) by the cofactor-independentphosphoglycerate mutase homologue BsnN, that is entirely distinctfrom the conventional biological C-As bond formation throughAs-alkylation of trivalent arsenic species by S-adenosylmethionine-dependentenzymes. Our findings will speed up the development of arsenic naturalproduct biosynthesis.

Automated summary

Recently, the unique bioactivities of arsenic-containing secondary metabolites have been discovered, but studies on arsenic secondary metabolism in microorganisms are limited. In this study, we focused on an unknown arsenic metabolite called bisenarsan, produced by well-studied actinomycetes, and elucidated its structure through feeding experiments and detailed NMR analyses. Bisenarsan is the first characterized arsenic secondary metabolite derived from actinomycetes and could potentially serve as a prototoxin or a detoxification product. We also confirmed the genes responsible for bisenarsan biosynthesis, particularly the (2-hydroxyethyl)arsonic acid moiety. Notably, we proposed a novel mechanism for the formation of a C-As bond in bisenarsan through intramolecular rearrangement by a phosphoglycerate mutase homologue, which is distinct from the conventional As-alkylation mechanism. Our findings will accelerate the development of arsenic natural product biosynthesis.