Avermectin biosynthesis: stable functional expression of branched chain α-keto acid dehydrogenase complex from Streptomyces avermitilis in Escherichia coli by selectively regulating individual subunit gene expression

To improve the production of short branched-chain acyl-CoAs for avermectin biosynthesis, the functional expression of the branched chain alpha-keto acid dehydrogenase complex (BKDH) from Streptomyces avermitilis was systematically optimized by selectively regulating individual subunit expression in Escherichia coli. Functional expression of the BKDH complex was achieved by independent and selective optimization of individual subunit genes of the complex. Codon optimization significantly improved the expression of complex component proteins BkdH and LpdA1 but expression of BkdF and BkdG depended on coexpression of the bkdH gene. The optimized BKDH complex supplied sufficient short branched-chain acyl-CoA to synthesize phlorisovalerophenone, a key intermediate in bitter acid (humulone) synthesis. We also developed a novel p15A origin-derived high-copy-number vector system for expression; the yield of PIVP was 350 ng/mOD. Through optimization strategies, we obtained stable, functional expression of the BKDH complex in E. coli, which could be applied in the heterologous production of numerous high-value-added chemicals, especially polyketides.