Site-directed mutagenesis reveals transition-state stabilization as a general catalytic mechanism for aminoacyl-tRNA synthetases
- 1 November 1987
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 26 (23), 7246-7250
- https://doi.org/10.1021/bi00397a008
Abstract
Some aminoacyl-tRNA synthetases of almost negligible homology do have a small region of similarity around the four-residue sequence His-Ile(or Leu or Met)-Gly-His-(or Asn), the HIGH sequence. The first histidine in this sequence in the tyrosyl-tRNA synthetase, His-45, has been shown to form part of a binding site for the .gamma.-phosphate of ATP in the transition state for the reaction as does Thr-40. Residue His-56 in the valyl-tRNA synthetase begins a HIGH sequence, and there is a threonine at position 52, one position closer to the histidine than in the tyrosyl-tRNA synthetase. The mutants Thr .fwdarw. Ala-52 and His .fwdarw. Asn-56 have been made and their complete free energy profiles for the formation of valyl adenylate determined. Difference energy diagrams have been constructed by comparison with the reaction of wild-type enzyme. The difference energy profiles are very similar to those for the mutants Thr .fwdarw. Ala-40 and His .fwdarw. Asn-45 of the tyrosyl-tRNA synthetase. Thr-52 and His-56 of the valyl-tRNA synthetase contribute little binding energy to valine, ATP, and Val-AMP. Instead, the wild-type enzyme binds the transition state and pyrophosphate some 6 kcal/mol more tightly than do the mutants. Preferential transition-state stabilization is thus an important component of catalysis by the valyl-tRNA synthetase. Further, by analogy to the tyrosyl-tRNA synthetase, the valyl-tRNA synthetase has a binding site for the .gamma.-phosphate of ATP in the transition state, and this is likely to be a general feature of aminoacyl-tRNA synthetases that have a HIGH region.This publication has 3 references indexed in Scilit:
- The valyl-tRNA synthetase from Bacillus stearothermophilus has considerable sequence homology with the isoleucyl-tRNA synthetase from Escherichia coliBiochemistry, 1987
- Site-directed mutagenesis as a probe of enzyme structure and catalysis: tyrosyl-tRNA synthetase cysteine-35 to glycine-35 mutationBiochemistry, 1983
- Ligand binding stoichiometries, subunit structure, and slow transitions in aminoacyl-tRNA synthetasesBiochemistry, 1977