Identification of Middle Chain Fatty Acyl-CoA Ligase Responsible for the Biosynthesis of 2-Alkylmalonyl-CoAs for Polyketide Extender Unit
作者:Takeshi Miyazawa、Shunji Takahashi、Akihiro Kawata、Suresh Panthee、Teruo Hayashi、Takeshi Shimizu、Toshihiko Nogawa、Hiroyuki Osada
DOI:10.1074/jbc.m115.677195
日期:2015.11
Background: Fatty acyl-CoA ligases involved in polyketide biosynthesis remain uncharacterized.Results: RevS classified in fatty acyl-AMP ligase clade was the middle chain fatty acyl-CoA ligase.Conclusion: RevS was responsible for 2-alkylmalonyl-CoA biosynthesis through enzyme coupling with RevT carboxylase/reductase.Significance: 2-Alkylmalonyl-CoA biosynthesis was strongly supported by the function of RevR and RevS, which utilized fatty acids derived from de novo biosynthesis and degradation products, respectively.Understanding the biosynthetic mechanism of the atypical polyketide extender unit is important for the development of bioactive natural products. Reveromycin (RM) derivatives produced by Streptomyces sp. SN-593 possess several aliphatic extender units. Here, we studied the molecular basis of 2-alkyl-malonyl- CoA formation by analyzing the revR and revS genes, which form a transcriptional unit with the revT gene, a crotonyl-CoA carboxylase/reductase homolog. We mainly focused on the uncharacterized adenylate-forming enzyme (RevS). revS gene disruption resulted in the reduction of all RM derivatives, whereas reintroduction of the gene restored the yield of RMs. Although RevS was classified in the fatty acyl-AMP ligase clade based on phylogenetic analysis, biochemical characterization revealed that the enzyme catalyzed the middle chain fatty acyl-CoA ligase (FACL) but not the fatty acyl-AMP ligase activity, suggesting the molecular evolution for acyl-CoA biosynthesis. Moreover, we examined the in vitro conversion of fatty acid into 2-alkylmalonyl-CoA using purified RevS and RevT. The coupling reaction showed efficient conversion of hexenoic acid into butylmalonyl-CoA. RevS efficiently catalyzed C8-C10 middle chain FACL activity; therefore, we speculated that the acyl-CoA precursor was truncated via beta-oxidation and converted into (E)-2-enoyl-CoA, a RevT substrate. To determine whether the beta-oxidation process is involved between the RevS and RevT reaction, we performed the feeding experiment using [1,2,3,4-C-13] octanoic acid. C-13 NMR analysis clearly demonstrated incorporation of the [3,4-C-13] octanoic acid moiety into the structure of RM-A. Our results provide insight into the role of uncharacterized RevS homologs that may catalyze middle chain FACL to produce a unique polyketide extender unit.