title: Role of lysine-195 in the KMSKS sequence of E. coli tryptophanyl-tRNA synthetase.
abstract: Lysine 195 in the K195 MSKS sequence of E. coli tryptophanyl-tRNA synthetase (TrpRS) was replaced with alanine. The resulting K195A mutant TrpRS had essentially unchanged Km values for ATP and Trp, but a 1500-fold decreased kcat in a pyrophosphate-ATP exchange reaction. This large decrease in kcat reduces the rate of aminoacyladenylate formation (step 1) to a rate comparable to the rate of aminoacylation of tRNA(Trp) (step 2) by the K195A mutant enzyme. Both the TIGN and KMSKS sequences are important for step 1 of class I aminoacyl-tRNA synthetase reactions.
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville 72701, USA.
authors.forename: K W
authors.initials: KW
authors.lastname: Chan
authors.forename: R E
authors.initials: RE
authors.lastname: Koeppe
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000409:Alanine; D000595:Amino Acid Sequence; D001483:Base Sequence; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008239:Lysine / Q000737:chemistry*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010710:Phosphates / Q000378:metabolism; D014369:Tryptophan-tRNA Ligase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D010710:Phosphates; D000255:Adenosine Triphosphate; D014369:Tryptophan-tRNA Ligase; D008239:Lysine; D000409:Alanine