title: Identification of the catalytic nucleophile of the family 29 alpha-L-fucosidase from Sulfolobus solfataricus via chemical rescue of an inactive mutant.
abstract: We have recently reported that a functional alpha-L-fucosidase could be expressed by a single insertional mutation in the region of overlap between the ORFs SSO11867 and SSO3060 of the hyperthermophilic Archaeon Sulfolobus solfataricus [Cobucci-Ponzano et al. J. Biol. Chem. (2003) 278, 14622-14631]. This enzyme, belonging to glycoside hydrolase family 29 (GH29), showed micromolar specificity for p-nitrophenyl-alpha-L-fucoside (pNp-Fuc) and promoted transfucosylation reactions by following a reaction mechanism in which the products retained the anomeric configuration of the substrate. The active site residues in GH29 enzymes are still unknown. We describe here the identification of the catalytic nucleophile of the reaction in the alpha-L-fucosidase from S. solfataricus by reactivation with sodium azide of the mutant Asp242Gly that shows a 10(3)-fold activity reduction on pNp-Fuc. The detailed stereochemical analysis of the fucosyl-azide produced by the mutant reactivated on pNp-Fuc revealed its inverted (beta-fucosyl azide) configuration compared with the substrate. This allows for the first time the unambiguous assignment of Asp242, and its homologous residues, as the nucleophilic catalytic residues of GH29 alpha-L-fucosidases. This is the first time that this approach is used for alpha-L-glycosidases, widening the applicability of this method.
authors.affiliation: Institute of Protein Biochemistry, Consiglio Nazionale delle Ricerche, Via P. Castellino 111, 80131, Naples, Italy.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Cobucci-Ponzano
authors.forename: Antonio
authors.initials: A
authors.lastname: Trincone
authors.forename: Assunta
authors.initials: A
authors.lastname: Giordano
authors.forename: Mosè
authors.initials: M
authors.lastname: Rossi
authors.forename: Marco
authors.initials: M
authors.lastname: Moracci
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001224:Aspartic Acid / Q000737:chemistry / Q000378:metabolism; D002236:Carbohydrate Conformation; D002384:Catalysis; D016384:Consensus Sequence; D004789:Enzyme Activation; D004795:Enzyme Stability; D006027:Glycosides / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D017386:Sequence Homology, Amino Acid; D019810:Sodium Azide / Q000737:chemistry / Q000494:pharmacology; D013237:Stereoisomerism; D016944:Sulfolobus / Q000201:enzymology*; D005644:alpha-L-Fucosidase / Q000235:genetics* / Q000378:metabolism
chemical_list: D006027:Glycosides; C014125:4-nitrophenylfucoside; D001224:Aspartic Acid; D019810:Sodium Azide; D005644:alpha-L-Fucosidase