1b4q | pdb_00001b4q
Solution structure of human thioltransferase complex with glutathione
Structural highlights
FunctionGLRX1_HUMAN Has a glutathione-disulfide oxidoreductase activity in the presence of NADPH and glutathione reductase. Reduces low molecular weight disulfides and proteins. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedHuman thioltransferase (TTase) is a 12 kDa thiol-disulfide oxidoreductase that appears to play a critical role in maintaining the redox environment of the cell. TTase acts as a potent and specific reducing agent for protein-S-S-glutathione mixed disulfides (protein-SSG) likely formed during oxidative stress or as redox intermediates in signal transduction pathways. Accordingly, the catalytic cycle of thioltransferase itself involves a covalent glutathionyl enzyme disulfide intermediate (TTase-C22-SSG). To understand the molecular basis of TTase specificity for the glutathione moiety, we engineered a quadruple Cys to Ser mutant of human TTase (C7S, C25S, C78S, and C82S) which retains only the active site cysteine residue (C22), and we solved its high-resolution NMR solution structure in the mixed disulfide intermediate with glutathione (QM-TTase-SSG). This mutant which cannot form a C22-S-S-C25 intramolecular disulfide displays the same catalytic efficiency (Vmax/KM) and specificity for glutathionyl mixed disulfide substrates as wild-type TTase, indicating that the Cys-25-SH moiety is not required for catalysis or glutathionyl specificity. The structure of human thioltransferase is characterized by a thioredoxin-like fold which comprises a four-stranded central beta-sheet flanked on each side by alpha-helices. The disulfide-adducted glutathione in the TTase-SSG complex has an extended conformation and is localized in a cleft near the protein surface encompassing the residues from helices-alpha2,alpha3, the active site loop, and the loop connecting helix-alpha3 and strand-beta3. Numerous van der Waals and electrostatic interactions between the protein and the glutathione moiety are identified as contributing to stabilization of the complex and confering the substrate specificity. Comparison of the human thioltransferase with other thiol-disulfide oxidoreductases reveals structural and functional differences. Reactivity of the human thioltransferase (glutaredoxin) C7S, C25S, C78S, C82S mutant and NMR solution structure of its glutathionyl mixed disulfide intermediate reflect catalytic specificity.,Yang Y, Jao S, Nanduri S, Starke DW, Mieyal JJ, Qin J Biochemistry. 1998 Dec 8;37(49):17145-56. PMID:9860827[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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