title: Ethylmalonyl coenzyme A mutase operates as a metabolic control point in Methylobacterium extorquens AM1.
abstract: The metabolism of one- and two-carbon compounds by the methylotrophic bacterium Methylobacterium extorquens AM1 involves high carbon flux through the ethylmalonyl coenzyme A (ethylmalonyl-CoA) pathway (EMC pathway). During growth on ethylamine, the EMC pathway operates as a linear pathway carrying the full assimilatory flux to produce glyoxylate, malate, and succinate. Assimilatory carbon enters the ethylmalonyl-CoA pathway directly as acetyl-CoA, bypassing pathways for formaldehyde oxidation/assimilation and the regulatory mechanisms controlling them, making ethylamine growth a useful condition to study the regulation of the EMC pathway. Wild-type M. extorquens cells were grown at steady state on a limiting concentration of succinate, and the growth substrate was then switched to ethylamine, a condition where the cell must make a sudden switch from utilizing the tricarboxylic acid (TCA) cycle to using the ethylmalonyl-CoA pathway for assimilation, which has been an effective strategy for identifying metabolic control points. A 9-h lag in growth was observed, during which butyryl-CoA, a degradation product of ethylmalonyl-CoA, accumulated, suggesting a metabolic imbalance. Ethylmalonyl-CoA mutase activity increased to a level sufficient for the observed growth rate at 9 h, which correlated with an upregulation of RNA transcripts for ecm and a decrease in the levels of ethylmalonyl-CoA. When the wild-type strain overexpressing ecm was tested with the same substrate switchover experiment, ethylmalonyl-CoA did not accumulate, growth resumed earlier, and, after a transient period of slow growth, the culture grew at a higher rate than that of the control. These findings demonstrate that ethylmalonyl-CoA mutase is a metabolic control point in the EMC pathway, expanding our understanding of its regulation.
authors.affiliation: Department of Microbiology, University of Washington, Seattle, Washington, USA nategood@uw.edu.
authors.forename: Nathan M
authors.initials: NM
authors.lastname: Good
authors.affiliation: Department of Chemical Engineering, University of Washington, Seattle, Washington, USA.
authors.forename: N Cecilia
authors.initials: NC
authors.lastname: Martinez-Gomez
authors.affiliation: Department of Chemical Engineering, University of Washington, Seattle, Washington, USA The eScience Institute, University of Washington, Seattle, Washington, USA.
authors.forename: David A C
authors.initials: DA
authors.lastname: Beck
authors.affiliation: Department of Microbiology, University of Washington, Seattle, Washington, USA Department of Chemical Engineering, University of Washington, Seattle, Washington, USA.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Lidstrom
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002952:Citric Acid Cycle; D005021:Ethylamines / Q000378:metabolism; D006038:Glyoxylates / Q000378:metabolism; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism*; D053858:Metabolic Networks and Pathways; D020601:Methylobacterium extorquens / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D001426:Bacterial Proteins; D005021:Ethylamines; D006038:Glyoxylates; C102829:ethylmalonyl-coenzyme A; D019751:Intramolecular Transferases; C031150:glyoxylic acid; C041564:ethylamine