Triggering of allostery in an enzyme by a point mutation: ornithine transcarbamoylase.
The origin of allostery is an unanswered question in the evolution of complex regulatory proteins. Anabolic ornithine transcarbamoylase, a trimer of identical subunits, is not an allosteric enzyme per se. However, when the active-site residue arginine-106 of the Escherichia coli enzyme is replaced with a glycine through site-directed mutagenesis, the resultant mutant enzyme manifests substrate cooperativity that is absent in the wild-type enzyme. Both homotropic and heterotropic interactions occur in the mutant enzyme. The initial velocity saturation curves of the substrates, carbamoyl phosphate and L-ornithine, conform to the Hill equation. The observed cooperativity depends on substrate but not enzyme concentration. The finding underscores the possibility that a single mutation of the enzyme in the cell could turn transcarbamoylation into a regulatory junction in the biosynthesis of L-arginine and urea.
Kuo
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LC
Department of Chemistry, Metcalf Center for Science and Engineering, Boston University, MA 02215.
Zambidis
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I
Caron
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D000494:Allosteric Regulation; D001665:Binding Sites; D002221:Carbamyl Phosphate / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D005998:Glycine; D007700:Kinetics; D046911:Macromolecular Substances; D009154:Mutation; D009952:Ornithine / Q000378:metabolism; D009954:Ornithine Carbamoyltransferase / Q000235:genetics* / Q000378:metabolism; D013329:Structure-Activity Relationship; D015032:Zinc / Q000494:pharmacology
D046911:Macromolecular Substances; D002221:Carbamyl Phosphate; D009952:Ornithine; D009954:Ornithine Carbamoyltransferase; D015032:Zinc; D005998:Glycine