Biosynthesis of the Monoguanidinated Inositol Moiety of Bluensomycin, a Possible Evolutionary Precursor of Streptomycin

Abstract

Abstract The general pattern of biosynthesis of the bluensidine (1D-1-O-carbamoyl-3-guanidino-3-deoxy-scyllo-inositol) moiety of bluensomycin, a monoguanidinated analogue of dihydrostreptomycin, has been studied in extracts of Streptomyces hygroscopicus forma glebosus ATCC 14607 (S. glebosus). Our results are consistent with the following biosynthetic pathway: myo-inositol (C)/→ keto-scyllo-inositol (D)/→ aminodeoxy-scyllo-inositol (E)/→ 1-amino-1-deoxy-scyllo-inositol-4-P (U)/→ 1D-1-O-carbamoyl-3-amino-3-deoxy-scyllo-inositol-6-P (F)/→ 1D-1-O-carbamoyl-3-guanidino-3-deoxy-scyllo-inositol-6-P →→ bluensomycin. A major uncertainty concerns the step (U) at which the carbamoyl group is introduced. Carbamoylation might occur, for example, prior to phosphorylation or following transamidination. myo-Inositol:NAD oxidoreductase activity (C) is reported for the first time in extracts of Streptomyces; activity was assayed by two radiochemical methods, both involving coupling with aminotransferase (D). l-Glutamine:keto-scyllo-inositol aminotransferase (D) was also found to catalyze aminodeoxy-scyllo-inositol:keto-scyllo-inositol, aminodeoxy-scyllo-inositol:pyruvate, and 1,3-diamino-1,3-dideoxy-scyllo-inositol:keto-scyllo-inositol transaminations. l-Arginine:inosamine-P amidinotransferase (F) catalyzed transamidinations with the following compounds as amidino acceptors: NH2OH, 1-amino-1-deoxy-scyllo-inositol-4-P, 1D-1-guanidino-3-amino-1,3-dideoxy-scyllo-inositol-6-P, 1D-1,3-diamino-1,3-dideoxy-scyllo-inositol-6-P, 1D-1,3-diamino-1,2,3-trideoxy-scyllo-inositol-6-P, and a compound present in S. glebosus extracts believed to be 1D-1-O-carbamoyl-3-amino-3-deoxy-scyllo-inositol-6-P. The latter transamidination is markedly enhanced in crude extracts by carbamoyl-P. S. glebosus extracts also have 1-guanidino-1-deoxy-scyllo-inositol-4-P phosphohydrolase activity; neither this enzyme nor the corresponding enzyme from streptomycin producers can dephosphorylate the transamidination product presumed to be bluensidine-6-P. Acid hydrolysis of the latter compound gave a compound which, unlike the unhydrolyzed compound, was converted to 1D-1-guanidino-3-amino-1,3-dideoxy-scyllo-inositol by enzymes from a streptomycin producing strain. S. glebosus cannot carry out the above conversion since it apparently lacks at least two enzymes which occur in streptomycin producers: guanidinodeoxy-(scyllo)-inositol dehydrogenase and l-alanine:1D-1-guanidino-3-keto-1-deoxy-scyllo-inositol aminotransferase. It is suggested that streptomycin producing strains might be descendents of an ancestral strain which, like S. glebosus, produced the monoguanidinated inositol derivative, bluensomycin. It is further suggested that gene duplication and subsequent evolutionary divergence resulted in biosynthesis of the diguanidinated inositol derivative, streptomycin, which is 10 times more effective than bluensomycin as an antibiotic and inhibitor of protein biosynthesis.