title: L-malyl-coenzyme A/beta-methylmalyl-coenzyme A lyase is involved in acetate assimilation of the isocitrate lyase-negative bacterium Rhodobacter capsulatus.
abstract: Cell extracts of Rhodobacter capsulatus grown on acetate contained an apparent malate synthase activity but lacked isocitrate lyase activity. Therefore, R. capsulatus cannot use the glyoxylate cycle for acetate assimilation, and a different pathway must exist. It is shown that the apparent malate synthase activity is due to the combination of a malyl-coenzyme A (CoA) lyase and a malyl-CoA-hydrolyzing enzyme. Malyl-CoA lyase activity was 20-fold up-regulated in acetate-grown cells versus glucose-grown cells. Malyl-CoA lyase was purified 250-fold with a recovery of 6%. The enzyme catalyzed not only the reversible condensation of glyoxylate and acetyl-CoA to L-malyl-CoA but also the reversible condensation of glyoxylate and propionyl-CoA to beta-methylmalyl-CoA. Enzyme activity was stimulated by divalent ions with preference for Mn(2+) and was inhibited by EDTA. The N-terminal amino acid sequence was determined, and a corresponding gene coding for a 34.2-kDa protein was identified and designated mcl1. The native molecular mass of the purified protein was 195 +/- 20 kDa, indicating a homohexameric composition. A homologous mcl1 gene was found in the genomes of the isocitrate lyase-negative bacteria Rhodobacter sphaeroides and Rhodospirillum rubrum in similar genomic environments. For Streptomyces coelicolor and Methylobacterium extorquens, mcl1 homologs are located within gene clusters implicated in acetate metabolism. We therefore propose that L-malyl-CoA/beta-methylmalyl-CoA lyase encoded by mcl1 is involved in acetate assimilation by R. capsulatus and possibly other glyoxylate cycle-negative bacteria.
authors.affiliation: Mikrobiologie, Institut Biologie II, Schänzlestr. 1, D-79104 Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Meister
authors.forename: Stephan
authors.initials: S
authors.lastname: Saum
authors.forename: Birgit E
authors.initials: BE
authors.lastname: Alber
authors.forename: Georg
authors.initials: G
authors.lastname: Fuchs
mesh_terms: D019342:Acetic Acid / Q000378:metabolism*; D000105:Acetyl Coenzyme A / Q000378:metabolism; D000214:Acyl Coenzyme A / Q000378:metabolism; D002413:Cations, Divalent / Q000494:pharmacology; D003067:Coenzymes / Q000494:pharmacology; D004269:DNA, Bacterial / Q000737:chemistry; D004492:Edetic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005798:Genes, Bacterial; D006038:Glyoxylates / Q000378:metabolism; D007522:Isocitrate Lyase / Q000378:metabolism; D020601:Methylobacterium extorquens / Q000235:genetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016366:Open Reading Frames; D007652:Oxo-Acid-Lyases / Q000302:isolation & purification / Q000378:metabolism*; D021122:Protein Subunits / Q000737:chemistry; D016354:Rhodobacter capsulatus / Q000201:enzymology* / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000235:genetics; D012247:Rhodospirillum rubrum / Q000235:genetics; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D017385:Sequence Homology; D048372:Streptomyces coelicolor / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D000214:Acyl Coenzyme A; D002413:Cations, Divalent; D003067:Coenzymes; D004269:DNA, Bacterial; D004791:Enzyme Inhibitors; D006038:Glyoxylates; D021122:Protein Subunits; C042519:malyl-coenzyme A; C009061:propionyl-coenzyme A; D000105:Acetyl Coenzyme A; D004492:Edetic Acid; D007652:Oxo-Acid-Lyases; C467898:beta-methylmalyl-coenzyme A lyase; D007522:Isocitrate Lyase; C021536:malyl-CoA lyase; C031150:glyoxylic acid; D019342:Acetic Acid