Identification of additional players in the alternative biosynthesis pathway to isovaleryl-CoA in the myxobacterium Myxococcus xanthus.
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.
Institut für Pharmazeutische Biotechnologie, Universität des Saarlandes, Saarbrücken, Germany.
Helge B
HB
Bode
Michael W
MW
Ring
Gertrud
G
Schwär
Matthias O
MO
Altmeyer
Carsten
C
Kegler
Ivy R
IR
Jose
Mitchell
M
Singer
Rolf
R
Müller
D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) / Q000235:genetics; D000214:Acyl Coenzyme A / Q000096:biosynthesis* / Q000378:metabolism; D055162:Biocatalysis; D003653:Decarboxylation; D020869:Gene Expression Profiling; D005798:Genes, Bacterial / Q000235:genetics; D006904:Hydroxymethylglutaryl-CoA Synthase / Q000378:metabolism*; D007930:Leucine / Q000096:biosynthesis; D009154:Mutation; D016941:Myxococcus xanthus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D009876:Operon; D010084:Oxidation-Reduction; D010641:Phenotype; D040901:Proteomics; D013729:Terpenes / Q000378:metabolism; D015854:Up-Regulation
D000214:Acyl Coenzyme A; D013729:Terpenes; C008047:3-hydroxy-3-methylglutaryl-coenzyme A; C017447:isovaleryl-coenzyme A; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D006904:Hydroxymethylglutaryl-CoA Synthase; D007930:Leucine