Identification of Additional Players in the Alternative Biosynthesis Pathway to Isovaleryl‐CoA in the Myxobacterium Myxococcus xanthus

Abstract

Isovaleryl-CoA (IV-CoA) is usually derived from the degradation of leucine by using the Bkd (branched-chain keto acid dehydrogenase) complex. We have previously identified an alternative pathway for IV-CoA formation in myxobacteria that branches from the well-known mevalonate-dependent isoprenoid biosynthesis pathway. We identified 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase (MvaS) to be involved in this pathway in Myxococcus xanthus, which is induced in mutants with impaired leucine degradation (e.g., bkd(-)) or during myxobacterial fruiting-body formation. Here, we show that the proteins required for leucine degradation are also involved in the alternative IV-CoA biosynthesis pathway through the efficient catalysis of the reverse reactions. Moreover, we conducted a global gene-expression experiment and compared vegetative wild-type cells with bkd mutants, and identified a five-gene operon that is highly up-regulated in bkd mutants and contains mvaS and other genes that are directly involved in the alternative pathway. Based on our experiments, we assigned roles to the genes required for the formation of IV-CoA from HMG-CoA. Additionally, several genes involved in outer-membrane biosynthesis and a plethora of genes encoding regulatory proteins were decreased in expression levels in the bkd(-) mutant; this explains the complex phenotype of bkd mutants including a lack of adhesion in developmental submerse culture.

Isoprenoids Are Essential for Fruiting Body Formation in Myxococcus xanthus

“…This second BKD activity might be a side activity of the pyruvate dehydrogenase or a related chemical oxidative decarboxylation, as no second bkd locus could be identified in the genome (unpublished results). Moreover, growth of HB002 is not MVL dependent because the block in the alternative pathway does not affect isoprenoid biosynthesis, as liuC encodes a dehydratase/hydratase that is involved in the conversion of HMG-CoA to 3-methylglutaconyl-CoA and vice versa (4). As expected, the FA profile (4) as well as the developmental phenotype (data not shown) can be complemented (Fig.…”

“…All (4), and FA analysis as well as myxobacterial fruiting body formation has also been described previously (26).…”

Identification of Functions Affecting Predator-Prey Interactions between Myxococcus xanthus and Bacillus subtilis

“…We speculate that the transporter mutant is unable to utilize BCAAs, preventing growth, and it therefore displays a deficiency in predation. Moreover, it has been shown that BCAAs, such as leucine, serve as the precursor for fatty acid biosynthesis and also as starter molecules for polyketide synthases (41,42). Reduced levels of available BCAAs due to disrup-tion of the ABC transporter could result in an altered specialized metabolite or fatty acid profile and generate deficits in growth on otherwise-suitable prey.…”

“…One of the most frequent transposon insertion sites (11 independent isolates) occurred in MXAN_5713, encoding an ABC transporter/permease predicted to be involved in branched-chain amino acid (BCAA) transport. BCAAs are essential to M. xanthus and function as precursors for fatty acid synthesis as well as specialized metabolite production (31,41,42). All 11 transposon insertion mutations in MXAN_5713 displayed an LOF phenotype (see Fig.…”

Engineered and Native Coenzyme B12-dependent Isovaleryl-CoA/Pivalyl-CoA Mutase

“…In addition, pivalic acid (or pivalyl-CoA) might be formed during catabolism of marine sponge-derived polytheonamides in which the tert-butyl modification of threonine is introduced post-translationally (28). Isovaleryl-CoA is produced during leucine catabolism via the branched chain keto acid dehydrogenase or in myxobateria, via a mevalonate-dependent isoprenoid biosynthesis pathway involving 3-hydroxy-3-methylglutaryl-CoA synthase (29). In several bacteria, the gene encoding IcmF is coregulated with those involved in branched-chain amino acid degradation (30) or fatty acid catabolism (13).…”