Enzymes harboring unnatural amino acids: mechanistic and structural analysis of the enhanced catalytic activity of a glutathione transferase containing 5-fluorotryptophan.Parsons, J.F., Xiao, G., Gilliland, G.L., Armstrong, R.N.
(1998) Biochemistry 37: 6286-6294
- PubMed: 9572843
- DOI: 10.1021/bi980219e
- PubMed Abstract:
- Contribution of Tyrosine 6 to the Catalytic Mechanism of Isoenzyme 3-3 of Glutathione S-Transferase
Liu, S.,Zhang, P.,Ji, X.,Johnson, W.W.,Gilliland, G.L.,Armstrong, R.N.
(1992) J.Biol.Chem. 267: 4296
- Tyrosine 115 Participates Both in Chemical and Physical Steps of the Catalytic Mechanism of a Glutathione S-Transferase
Johnson, W.W.,Liu, S.,Ji, X.,Gilliland, G.L.,Armstrong, R.N.
(1993) J.Biol.Chem. 268: 11508
- The Three-Dimensional Structure of a Glutathione S-Transferase from the Mu Gene Class. Structural Analysis of the Binary Complex of Isoenzyme 3-3 and Glutathione at 2.2-A Resolution
Ji, X.,Zhang, P.,Armstrong, R.N.,Gilliland, G.L.
(1992) Biochemistry 31: 10169
The catalytic characteristics and structure of the M1-1 isoenzyme of rat glutathione (GSH) transferase in which all four tryptophan residues in each monomer are replaced with 5-fluorotryptophan are described. The fluorine-for-hydrogen substitution do ...
The catalytic characteristics and structure of the M1-1 isoenzyme of rat glutathione (GSH) transferase in which all four tryptophan residues in each monomer are replaced with 5-fluorotryptophan are described. The fluorine-for-hydrogen substitution does not change the interaction of the enzyme with GSH even though two tryptophan residues (Trp7 and Trp45) are involved in direct hydrogen-bonding interactions with the substrate. The rate constants for association and dissociation of the peptide, measured by stopped-flow spectrometry, remain unchanged by the unnatural amino acid. The 5-FTrp-substituted enzyme exhibits a kcat of 73 s-1 as compared to 18 s-1 for the native enzyme toward 1-chloro-2,4-dinitrobenzene. That the increase in the turnover number is due to an enhanced rate of product release in the mutant is confirmed by the kinetics of the approach to equilibrium for binding of the product. The crystal structure of the 5-FTrp-containing enzyme was solved at a resolution of 2.0 A by difference Fourier techniques. The structure reveals local conformational changes in the structural elements that define the approach to the active site which are attributed to steric interactions of the fluorine atoms associated with 5-FTrp146 and 5-FTrp214 in domain II. These changes appear to result in the enhanced rate of product release. This structure represents the first of a protein substituted with 5-fluorotryptophan.
Departments of Biochemistry and Chemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.