Anthracycline biosynthesis involves the construction of an aglycone core (by a
type II polyketide synthase) to which one or more sugar residues are attached. Nogalamycin consists of three components: • nogalamycinone (black), the aglycone core • nogalose (magenta) • nogalamine (green) Each component is built separately and then ligated together by a two glycosyltransferases. All of the machinery associated with the biosynthesis of nogalamycin are located within the same biosynthetic gene cluster of
S. nogalater.
Nogalamycinone biosynthesis The biosynthetic pathway towards the aglycone core of nogalamycin has been determined by a combination of bioinformatic analysis and cloning of individual components of the biosynthetic pathway. The biosynthetic route is similar to that of aklavinone (the aglycone core of most anthracyclines, including
doxorubicin), the sole difference being that the first acyl group that is loaded into the PKS is an acetate rather than a propionate. The following genes are involved in the biosynthesis of the core nogalamycinone species: •
snoa1 (ketosynthase-α) •
snoa2 (ketosynthase-β chain length factor) •
snoa3 (acyl carrier protein) •
snoaD (ketoreductase) •
snoaE (aromatase) •
snoaM (cyclase) •
snoaB (oxygenase) •
snoaC (methyltransferase) •
snoaL (cyclase) •
snoaF (ketoreductase)
Nogalamine and nogalose biosynthesis The sugar moieties that are attached to nogalamycinone are produced from
glucose-1-phosphate. Although the steps following dTDP-4-keto-6-deoxyglucose have not been confirmed
in vitro, the high degree of sequence similarity with homologous enzymes from other organisms suggests that the mechanism proceeds as detailed at right. The following enzymes are involved in the biosynthesis of nogalamine and nogalose: more recent data suggest that the nogalose moiety on nogalamycin is methylated after the nogalamycinone core has been glycosylated.
Nogalamycinone glycosylation and tailoring The most noteworthy aspect of the structure of nogalamycin is the dual attachment of nogalamine both through
O-glycosylation and also through a carbon-carbon bond at the C2 position of the nogalamycinone core, The following enzymes are involved in the final tailoring steps of nogalamycin.
SnoN and
snoT are genes in the nogalamycin gene cluster that are likely to catalyze the final hydroxylation: •
snogE (glycosyltransferase) •
snoaL2 (hydroxylase) •
snogY (O-methyltransferase) •
snogM (putative O-methyltransferase) •
snogL (putative O-methyltransferase) •
snogD (glycosyltransferase) •
snoN/T ==References==