期刊
ACS CHEMICAL BIOLOGY
卷 13, 期 12, 页码 3385-3395出版社
AMER CHEMICAL SOC
DOI: 10.1021/acschembio.8b00910
关键词
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资金
- Margaret J. Hunter Collegiate Professorship
- St. Petersburg State University Grant [15.61.951.2015]
- [GM107550-03]
- [NIH GM118815-01A1]
- [NIH CA108874]
- [NIH GM067550]
- [NIH RO1 DK042303]
Dozens of type A malyngamides, principally identified by a decorated six-membered cyclohexanone head group and methoxylated lyngbic acid tail, have been isolated over several decades. Their environmental sources include macro- and microbiotic organisms, including sea hares, red alga, and cyanobacterial assemblages, but the true producing organism has remained enigmatic. Many type A analogues display potent bioactivity in human-health related assays, spurring an interest in this molecular class and its biosynthetic pathway. Here, we present the discovery of the type A malyngamide biosynthetic pathway in the first sequenced genome of the cyanobacterial genus Okeania. Bioinformatic analysis of two cultured Okeania genome assemblies identified 62 and 68 kb polyketide synthase/nonribosomal peptide synthetase (PKS/NRPS) pathways with unusual loading and termination genes. NMR data of malyngamide C acetate derived from C-13-substrate-fed cultures provided evidence that an intact octanoate moiety is transferred to the first KS module via a LipM homologue originally associated with lipoic acid metabolism and implicated an inactive ketoreductase (KR0) as critical for six-membered ring formation, a hallmark of the malyngamide family. Phylogenetic analysis and homology modeling of the penultimate KR0 domain inferred structural cofactor binding and active site alterations as contributory to domain dysfunction, which was confirmed by recombinant protein expression and NADPH binding assay. The carbonyl retained from this KR0 ultimately enables an intramolecular Knoevenagel condensation to form the characteristic cyclohexanone ring. Understanding this critical step allows assignment of a biosynthetic model for all type A malyngamides, whereby well-characterized tailoring modifications explain the surprising proliferation and diversity of analogues.
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