Contribution of active site glutamine to rate enhancement in ubiquitin C-terminal hydrolases.

ABSTRACT: Ubiquitin C-terminal hydrolases (UCHs) are cysteine proteases featuring a classical Cys-His-Asp catalytic triad, and also a highly conserved Gln that is thought to be a part of the oxyanion hole. However, the contribution of this side chain to catalysis by UCHs is not known. Herein, we demonstrate that the Gln side chain contributes to rate enhancement in UCHL1, UCHL3, and UCHL5. Mutation of the Gln to Ala in these enzymes impairs the catalytic efficiency, mainly because of a 16-fold to 30-fold reduction in k(cat) , which is consistent with a loss of approximately 2 kcal·mol(-1) in transition state stabilization. However, the contribution to transition state stabilization observed here is rather modest for the side chain's role in oxyanion stabilization. Interestingly, we discovered that t

SUBMITTER: Boudreaux DA 

PROVIDER: S-EPMC3410986 | biostudies-literature | 2012 Mar

REPOSITORIES: biostudies-literature