The Apparent Malate Synthase Activity of Rhodobacter sphaeroides Is Due to Two Paralogous Enzymes, (3 S )-Malyl-Coenzyme A (CoA)/β-Methylmalyl-CoA Lyase and (3 S )- Malyl-CoA Thioesterase
| Autor: | Georg Fuchs, Birgit E. Alber, Tobias J. Erb, Lena Frerichs-Revermann |
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| Rok vydání: | 2010 |
| Předmět: | |
| Zdroj: | Journal of Bacteriology. 192:1249-1258 |
| ISSN: | 1098-5530 0021-9193 |
| DOI: | 10.1128/jb.01267-09 |
| Popis: | 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 (3 S )-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 β-methylmalyl-CoA into glyoxylate and propionyl-CoA during acetyl-CoA assimilation. In contrast, Mcl2 was shown to be the sought (3 S )-malyl-CoA thioesterase in the ethylmalonyl-CoA pathway, which specifically hydrolyzes (3 S )-malyl-CoA but does not use β-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. |
| Databáze: | OpenAIRE |
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