title: Properties of the Escherichia coli rhodanese-like protein SseA: contribution of the active-site residue Ser240 to sulfur donor recognition.
abstract: The product of Escherichia coli sseA gene (SseA) was the subject of the present investigation aimed to provide a tool for functional classification of the bacterial proteins of the rhodanese family. E. coli SseA contains the motif CGSGVTA around the catalytic cysteine (Cys238). In eukaryotic sulfurtransferases this motif discriminates for 3-mercaptopyruvate:cyanide sulfurtransferase over thiosulfate:cyanide sulfurtransferases (rhodanese). The biochemical characterization of E. coli SseA allowed the identification of the first prokaryotic protein with a preference for 3-mercaptopyruvate as donor substrate. Replacement of Ser240 with Ala showed that the presence of a hydrophobic residue did not affect the binding of 3-mercaptopyruvate, but strongly prevented thiosulfate binding. On the contrary, substitution of Ser240 with an ionizable residue (Lys) increased the affinity for thiosulfate.
authors.affiliation: Dipartimento Scienze Molecolari Agroalimentari, Università di Milano, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Colnaghi
authors.forename: G
authors.initials: G
authors.lastname: Cassinelli
authors.forename: M
authors.initials: M
authors.lastname: Drummond
authors.forename: F
authors.initials: F
authors.lastname: Forlani
authors.forename: S
authors.initials: S
authors.lastname: Pagani
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D001665:Binding Sites / Q000502:physiology; D002384:Catalysis; D003545:Cysteine / Q000031:analogs & derivatives / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology*; D008024:Ligands; D016297:Mutagenesis, Site-Directed; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013379:Substrate Specificity / Q000502:physiology; D013466:Sulfurtransferases / Q000737:chemistry* / Q000235:genetics; D013884:Thiosulfate Sulfurtransferase / Q000737:chemistry / Q000235:genetics; D013885:Thiosulfates / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D013885:Thiosulfates; C008366:3-mercaptopyruvic acid; D013466:Sulfurtransferases; D013884:Thiosulfate Sulfurtransferase; C021550:3-mercaptopyruvate sulphurtransferase; D003545:Cysteine