Ribosylhopane,a Novel Bacterial Hopanoid,as Precursor of C35 Bacteriohopanepolyols in Streptomyces coelicolor A3(2)

Wild‐type Streptomyces coelicolor A3(2) produces aminobacteriohopanetriol as the only elongated C₃₅ hopanoid. The hopanoid phenotype of two mutants bearing a deletion of genes from a previously identified hopanoid biosynthesis gene cluster provides clues to the formation of C₃₅ bacteriohopanepolyols. orf14 encodes a putative nucleosidase; its deletion induces the accumulation of adenosylhopane as it cannot be converted into ribosylhopane. orf18 encodes a putative transaminase; its deletion results in the accumulation of adenosylhopane, ribosylhopane, and bacteriohopanetetrol. Ribosylhopane was postulated twenty years ago as a precursor for bacterial hopanoids but was never identified in a bacterium. Absence of the transaminase encoded by orf18 prevents the reductive amination of ribosylhopane into aminobacteriohopanetriol and induces its accumulation. Its reduction by an aldose‐reductase‐like enzyme produces bacteriohopanetetrol, which is normally not present in S. coelicolor.