title: Evolution of the C30 carotenoid synthase CrtM for function in a C40 pathway.
abstract: The C30 carotene synthase CrtM from Staphylococcus aureus and the C40 carotene synthase CrtB from Erwinia uredovora were swapped into their respective foreign C40 and C30 biosynthetic pathways (heterologously expressed in Escherichia coli) and evaluated for function. Each displayed negligible ability to synthesize the natural carotenoid product of the other. After one round of mutagenesis and screening, we isolated 116 variants of CrtM able to synthesize C40 carotenoids. In contrast, we failed to find a single variant of CrtB with detectable C30 activity. Subsequent analysis revealed that the best CrtM mutants performed comparably to CrtB in an in vivo C40 pathway. These mutants showed significant variation in performance in their original C30 pathway, indicating the emergence of enzymes with broadened substrate specificity as well as those with shifted specificity. We discovered that Phe 26 alone determines the specificity of CrtM. The plasticity of CrtM with respect to its substrate and product range highlights the potential for creating further new carotenoid backbone structures.
authors.affiliation: Department of Chemical Engineering, California Institute of Technology 210-41, Pasadena, California 91125, USA. umeno@cheme.caltech.edu
authors.forename: Daisuke
authors.initials: D
authors.lastname: Umeno
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Tobias
authors.forename: Frances H
authors.initials: FH
authors.lastname: Arnold
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000096:biosynthesis*; D004885:Erwinia / Q000201:enzymology* / Q000235:genetics; D019143:Evolution, Molecular; D013186:Farnesyl-Diphosphate Farnesyltransferase / Q000235:genetics* / Q000378:metabolism; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D016296:Mutagenesis; D009154:Mutation; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D002338:Carotenoids; C091056:CrtM protein, Staphylococcus aureus; D019883:Alkyl and Aryl Transferases; D013186:Farnesyl-Diphosphate Farnesyltransferase; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase