3-Hydroxy-3-methylglutaryl-coenzyme A (CoA) synthase is involved in biosynthesis of isovaleryl-CoA in the myxobacterium Myxococcus xanthus during fruiting body formation

Abstract

Isovaleryl-coenzyme A (IV-CoA) is the starting unit for some secondary metabolites and iso-odd fatty acids in several bacteria. According to textbook biochemistry, IV-CoA is derived from leucine degradation, but recently an alternative pathway that branches from the well-known mevalonate-dependent isoprenoid biosynthesis has been described for myxobacteria. A double mutant was constructed in Myxococcus xanthus by deletion of genes involved in leucine degradation and disruption of mvaS encoding the 3-hydroxy-3-methylglutaryl-coenzyme A synthase. A dramatic decrease of IV-CoA-derived iso-odd fatty acids was observed for the mutant, confirming mvaS to be involved in the alternative pathway. Additional quantitative real-time reverse transcription-PCR experiments indicated that mvaS is transcriptionally regulated by isovalerate. Furthermore, feeding studies employing an intermediate specific for the alternative pathway revealed that this pathway is induced during fruiting body formation, which presumably increases the amount of IV-CoA available when leucine is limited.

FIG. 1.

Biosynthesis of IV-CoA and isoprenoids in myxobacteria. Dashed arrows indicate multistep reactions. MvaS, 3-hydroxy-3-methylglutaryl-CoA synthase; Bkd, branched-chain keto acid dehydrogenase complex.

FIG. 2.

HMG-CoA transcript numbers (filled symbols) during vegetative growth (open symbols) of M. xanthus DK1622 (wild type; ▴), DK5643 (Δbkd; ▪), DK5643 plus 1 mM IVA (•), and DK5643 plus 1 mM IVA (IVA-supplemented preculture; ⧫). Mean values of two to three independent experiments are shown, with error bars representing the data ranges.