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Effect of A New Ionic Pair on the Unfolding Activation Barrier of α- Glucosidase B

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Thermal unfolding kinetics of β-glucosidase B from Paenibacillus polymyxa and its thermoresistant mutant H62R were determined from far-UV circular dichroism (CD) measurements at different temperatures. The unfolding of both enzymes followed simple two-state kinetics. The new ionic pair formed between Arg62 and Glu429 in the H62R variant did not change substantially the enzyme structure as judged by far-UV CD and fluorescence spectra, but produced an increase in the unfolding activation barrier of 0.95 ± 0.10 kcal mol-1, in good agreement with the energetic contribution reported for surface salt bridges in proteins. Eyring's analysis of the unfolding kinetic constants showed that the activation enthalpies for thermal denaturation of both enzymes were essentially the same. Thus, the greater kinetic stability rendered by the salt bridge seems to be due to A reduction in the activation entropy.

Keywords: Activation entropy; hydration entropy; salt bridge; thermal unfolding kinetics; transition state

Document Type: Research Article


Affiliations: Departamento de Quimica, Universidad Autonoma Metropolitana-Iztapalapa, Apartado Postal 55-534, Iztapalapa D.F. 09340, Mexico.

Publication date: 2006-02-01

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  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
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