Pikromycin

Pikromycin was studied by Brokmann and Hekel in 1951 and was the first antibiotic macrolide to be isolated. Pikromycin is synthesized through a type I polyketide synthase system in Streptomyces venezuelae, a species of Gram-positive bacterium in the genus Streptomyces. Pikromycin is derived from narbonolide, a 14-membered ring macrolide. Along with the narbonolide backbone, pikromycin includes a desosamine sugar and a hydroxyl group. Although Pikromycin is not a clinically useful antibiotic, it can be used as a raw material to synthesize antibiotic ketolide compounds such as ertythromycins and new epothilones.

Biosynthesis
The pikromycin polyketide synthase of Streptomyces venezuelae contains four polypeptides: PikAI, PikAII, PikAIII, and PikAIV. These polypeptides contain a loading module, six extension molecules, and a thioesterase domain that terminated the biosynthetic procedure. Recently electron cryo-microscopy have been used to determine sub-nanometre-resolution three- dimensional reconstructions of a full-length PKS module from the bacterium Streptomyces venezuelae that revealed an unexpectedly different architecture. In Figure 1, each circle corresponds to a PKS mutilifuctional protein, where ACP is acyl carrier protein, KS is keto-ACP synthase, KSQ is a keto-ACP synthase like domain, AT is acyltransferase, KR is keto ACP reductase, KR with cross is inactive KR, DH is hydroxyl-thioester dehydratase, ER is enoyl reductase, TEI is thioesterase domain I, TEII is type II thioesterase. Des corresponds to the enzymes utilized in desosamine biosynthesis and transfer, which include DesI-DesVIII.

Figure 2 represents the desosamine deoxyamino sugar biosynthetic pathway. DesI-DesVI (des locus of pikromycin PKS) encodes all the enzymes needed to obtain TDP-desoamine from TDP-glucose. DesVII and DesVIII activities transfer desoamine to narbonolide and narbomycin is obtained. PikC cytochrome P450 hydrolase catalyzes the hydroxylation of narbomycin to obtain pikromycin.