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Differential effects on transition-state stabilization, substrate saturation and catalytic turnover by unnatural amino acid residues in a glutathione-binding loop of human GST P1-1
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Biochemistry.
Manuscript (Other academic)
URN: urn:nbn:se:uu:diva-94867OAI: oai:DiVA.org:uu-94867DiVA: diva2:168871
Available from: 2006-09-25 Created: 2006-09-25 Last updated: 2010-01-13Bibliographically approved
In thesis
1. Structure-Function Relationships of Pi Class Glutathione Transferase Studied by Protein Engineering
Open this publication in new window or tab >>Structure-Function Relationships of Pi Class Glutathione Transferase Studied by Protein Engineering
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The glutathione transferases (GSTs) represent a superfamily of dimeric proteins involved in cellular detoxication by catalyzing the nucleophilic addition of the reduced glutathione (GSH) to the hydrophobic electrophiles. The present work focuses on the functional role of the conserved structures of GSTP1-1. The lock-and-key motif is a highly conserved hydrophobic interaction in the subunit interface of Pi, Mu, and Alpha class GSTs. The key residue (Tyr50 in hGSTP1-1) of one subunit is wedged into a hydrophobic pocket of the neighboring subunit. The heterodimer GSTP1/Y50A was constructed from the fully active wild-type GSTP1-1 and the nearly inactive Y50A in order to study how an essentially inactive subunit influences the activity of the neighboring subunit. The results illuminate the vital role of the lock-and-key motif in modulating the GSH binding and the rate of catalysis. Additionally, the two active sites of the dimeric enzyme work synergistically. An observed water network, in hGSTP1-1 structures, connects the two active sites, thereby offering a mechanism for communication between the two active sites.

Cys48 and Tyr50 were targeted by mutations and chemical modifications for understanding how the α2 loop residues modulate GSH binding and catalysis. The replacement of Tyr50 with different unnatural amino acids showed that the nature of the key residue side-chain influences the interaction with the lock structure and, consequently, the catalytic activity. The KMGSH, GSH affinity and protein stability can be modulated by fitting key residue into the lock cavity of the neighbor subunit and, consequently, restriction of the flexibility of the α2 loop. Optimization of the interaction between the key residue and the lock-cavity increases kcat. Also, the crystal structure of the Cys-free variant was determined. The result indicated that Cys48 restricts the flexibility of the α2 loop by interacting with surrounding residues and, consequently, contributes to GSH binding and protein stability.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 67 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 222
Biochemistry, Glutathione transferase, targeted chemical modification, lock-and-key motif, cooperativity, stucture-function relationship, protein engineering, unnatural amino acid, site-specific mutation, Biokemi
urn:nbn:se:uu:diva-7146 (URN)91-554-6654-0 (ISBN)
Public defence
2006-10-16, B42, BMC, Uppsala University, Uppsala, 10:15
Available from: 2006-09-25 Created: 2006-09-25Bibliographically approved

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