The first step of aminoacylation at the atomic level in histidyl-tRNA synthetase.

ABSTRACT: The crystal structure of an enzyme-substrate complex with histidyl-tRNA synthetase from Escherichia coli, ATP, and the amino acid analog histidinol is described and compared with the previously obtained enzyme-product complex with histidyl-adenylate. An active site arginine, Arg-259, unique to all histidyl-tRNA synthetases, plays the role of the catalytic magnesium ion seen in seryl-tRNA synthetase. When Arg-259 is substituted with histidine, the apparent second order rate constant (kcat/Km) for the pyrophosphate exchange reaction and the aminoacylation reaction decreases 1,000-fold and 500-fold, respectively. Crystals soaked with MnCl2 reveal the existence of two metal binding sites between beta- and gamma-phosphates; these sites appear to stabilize the conformation of the pyrophosphate.

SUBMITTER: Arnez JG 

PROVIDER: S-EPMC23771 | biostudies-literature | 1997 Jul

REPOSITORIES: biostudies-literature