title: Synthesis of C5-dicarboxylic acids from C2-units involving crotonyl-CoA carboxylase/reductase: the ethylmalonyl-CoA pathway.
abstract: Fifty years ago, Kornberg and Krebs established the glyoxylate cycle as the pathway for the synthesis of cell constituents from C2-units. However, since then, many bacteria have been described that do not contain isocitrate lyase, the key enzyme of this pathway. Here, a pathway termed the ethylmalonyl-CoA pathway operating in such organisms is described. Isotopically labeled acetate and bicarbonate were transformed to ethylmalonyl-CoA by cell extracts of acetate-grown, isocitrate lyase-negative Rhodobacter sphaeroides as determined by NMR spectroscopy. Crotonyl-CoA carboxylase/reductase, catalyzing crotonyl-CoA + CO2 + NADPH --> ethylmalonyl-CoA- + NADP+ was identified as the key enzyme of the ethylmalonyl-CoA pathway. The reductive carboxylation of an enoyl-thioester is a unique biochemical reaction, unprecedented in biology. The enzyme from R. sphaeroides was heterologously produced in Escherichia coli and characterized. Crotonyl-CoA carboxylase/reductase (or its gene) can be used as a marker for the presence of the ethylmalonyl-CoA pathway, which functions not only in acetyl-CoA assimilation. In Streptomyces sp., it may also supply precursors (ethylmalonyl-CoA) for antibiotic biosynthesis. For methylotrophic bacteria such as Methylobacterium extorquens, extension of the serine cycle with reactions of the ethylmalonyl-CoA pathway leads to a simplified scheme for isocitrate lyase-independent C1 assimilation.
authors.affiliation: Mikrobiologie, Institut für Biologie II, Fakultät für Chemie, Pharmazie und Geowissenschaften, Albert-Ludwigs-Universität Freiburg, Schänzlestrasse 1, 79104 Freiburg, Germany.
authors.forename: Tobias J
authors.initials: TJ
authors.lastname: Erb
authors.forename: Ivan A
authors.initials: IA
authors.lastname: Berg
authors.forename: Volker
authors.initials: V
authors.lastname: Brecht
authors.forename: Michael
authors.initials: M
authors.lastname: Müller
authors.forename: Georg
authors.initials: G
authors.lastname: Fuchs
authors.forename: Birgit E
authors.initials: BE
authors.lastname: Alber
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000096:biosynthesis; D002262:Carboxy-Lyases / Q000378:metabolism*; D002846:Chromatography, Affinity; D002848:Chromatography, DEAE-Cellulose; D002851:Chromatography, High Pressure Liquid; D003998:Dicarboxylic Acids / Q000737:chemistry / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D020601:Methylobacterium extorquens / Q000201:enzymology; D008954:Models, Biological; D019906:Nuclear Magnetic Resonance, Biomolecular; D010088:Oxidoreductases / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000201:enzymology; D013302:Streptomyces / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D000900:Anti-Bacterial Agents; D003998:Dicarboxylic Acids; C102829:ethylmalonyl-coenzyme A; C010701:crotonyl-coenzyme A; D010088:Oxidoreductases; D002262:Carboxy-Lyases