The apparent malate synthase activity of Rhodobacter sphaeroides is due to two paralogous enzymes, (3S)-Malyl-coenzyme A (CoA)/{beta}-methylmalyl-CoA lyase and (3S)- Malyl-CoA thioesterase.
Assimilation of acetyl coenzyme A (acetyl-CoA) is an essential process in many bacteria that proceeds via the glyoxylate cycle or the ethylmalonyl-CoA pathway. In both assimilation strategies, one of the final products is malate that is formed by the condensation of acetyl-CoA with glyoxylate. In the glyoxylate cycle this reaction is catalyzed by malate synthase, whereas in the ethylmalonyl-CoA pathway the reaction is separated into two proteins: malyl-CoA lyase, a well-known enzyme catalyzing the Claisen condensation of acetyl-CoA with glyoxylate and yielding malyl-CoA, and an unidentified malyl-CoA thioesterase that hydrolyzes malyl-CoA into malate and CoA. In this study the roles of Mcl1 and Mcl2, two malyl-CoA lyase homologs in Rhodobacter sphaeroides, were investigated by gene inactivation and biochemical studies. Mcl1 is a true (3S)-malyl-CoA lyase operating in the ethylmalonyl-CoA pathway. Notably, Mcl1 is a promiscuous enzyme and catalyzes not only the condensation of acetyl-CoA and glyoxylate but also the cleavage of beta-methylmalyl-CoA into glyoxylate and propionyl-CoA during acetyl-CoA assimilation. In contrast, Mcl2 was shown to be the sought (3S)-malyl-CoA thioesterase in the ethylmalonyl-CoA pathway, which specifically hydrolyzes (3S)-malyl-CoA but does not use beta-methylmalyl-CoA or catalyze a lyase or condensation reaction. The identification of Mcl2 as thioesterase extends the enzyme functions of malyl-CoA lyase homologs that have been known only as "Claisen condensation" enzymes so far. Mcl1 and Mcl2 are both related to malate synthase, an enzyme which catalyzes both a Claisen condensation and thioester hydrolysis reaction.
Erb
Tobias J
TJ
Department of Microbiology, Ohio State University, 484 West 12th Ave., Room 417, Columbus, OH 43210, USA.
Frerichs-Revermann
Lena
L
Fuchs
Georg
G
Alber
Birgit E
BE
D000105:Acetyl Coenzyme A / Q000378:metabolism; D000214:Acyl Coenzyme A / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D055786:Gene Knockout Techniques; D006038:Glyoxylates / Q000378:metabolism; D008292:Malate Synthase / Q000378:metabolism*; D053858:Metabolic Networks and Pathways / Q000235:genetics; D008969:Molecular Sequence Data; D007652:Oxo-Acid-Lyases / Q000235:genetics / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D013869:Thiolester Hydrolases / Q000235:genetics / Q000378:metabolism*
D000214:Acyl Coenzyme A; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D006038:Glyoxylates; C042519:malyl-coenzyme A; C009061:propionyl-coenzyme A; D000105:Acetyl Coenzyme A; D008292:Malate Synthase; D013869:Thiolester Hydrolases; D007652:Oxo-Acid-Lyases; C467898:beta-methylmalyl-coenzyme A lyase; C031150:glyoxylic acid