A new family of glucose-1-phosphate/glucosamine-1-phosphate nucleotidylyltransferase in the biosynthetic pathways for antibiotics

Aminoglycoside antibiotics are composed of aminosugars and a unique aminocyclitol aglycon including 2-deoxystreptamine (DOS), streptidine, actinamine, etc., and nucleotidylyltransferases, sugar modifying enzymes, and glycosyltransferases appear to be essential for their biosynthesis. However, the genes encoding those enzymes were unable to be identified by a standard homology search in the butirosin biosynthetic btr gene cluster, except that the btrM gene appeared to be a glycosyltransfease. Disruption studies of the btrD gene indicated that BtrD was involved in the supply of a glycosyl donor immediately prior to the glycosylation of DOS giving paromamine. As anticipated, BtrD expressed in Escherichia coli was able to catalyze UDP-D-glucosamine formation from D-glucosamine-1-phosphate and UTP. Both dTTP and UTP were good NTP substrates, and D-glucose-1-phosphate and D-glucosamine-1-phosphate were good sugar phosphates for the enzyme reaction. This finding is the first to identify an enzyme which activates a sugar donor in the DOS-containing antibiotics. Interestingly, BtrD homologues have been reported as functionally unknown open reading frames (ORFs) in the biosynthetic gene clusters for several antibiotics including teicoplanin, balhimycin, chloroeremomycin, and mitomycin C. It appears therefore that gene clusters for antibiotic biosynthesis provide their own nucleotidylyltransferases, and the BtrD homologues are among the secondary metabolism specific enzymes.