Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 65325
Title Improving low-temperature catalysis in the hyperthermostable Pyrococcus furiosus b-glucosidase CelB by directed evolution
Author(s) Lebbink, J.H.G.; Kaper, T.; Bron, P.; Oost, J. van der; Vos, W.M. de
Source Biochemistry 39 (2000). - ISSN 0006-2960 - p. 3656 - 3665.
Department(s) Microbiology
Publication type Refereed Article in a scientific journal
Publication year 2000
Abstract The -glucosidase from the hyperthermophilic archaeon Pyrococcus furiosus (CelB) is the most thermostable and thermoactive family 1 glycosylhydrolase described to date. To obtain more insight in the molecular determinants of adaptations to high temperatures and study the possibility of optimizing low-temperature activity of a hyperthermostable enzyme, we generated a library of random CelB mutants in Escherichia coli. This library was screened for increased activity on p-nitrophenyl--D-glucopyranoside at room temperature. Multiple CelB variants were identified with up to 3-fold increased rates of hydrolysis of this aryl glucoside, and 10 of them were characterized in detail. Amino acid substitutions were identified in the active-site region, at subunit interfaces, at the enzyme surface, and buried in the interior of the monomers. Characterization of the mutants revealed that the increase in low-temperature activity was achieved in different ways, including altered substrate specificity and increased flexibility by an apparent overall destabilization of the enzyme. Kinetic characterization of the active-site mutants showed that in all cases the catalytic efficiency at 20 C on p-nitrophenyl--D-glucose, as well as on the disaccharide cellobiose, was increased up to 2-fold. In most cases, this was achieved at the expense of -galactosidase activity at 20 C and total catalytic efficiency at 90 C. Substrate specificity was found to be affected by many of the observed amino acid substitutions, of which only some are located in the vicinity of the active site. The largest effect on substrate specificity was observed with the CelB variant N415S that showed a 7.5-fold increase in the ratio of p-nitrophenyl--D-glucopyranoside/p-nitrophenyl--D-galactopyranoside hydrolysis. This asparagine at position 415 is predicted to interact with active-site residues that stabilize the hydroxyl group at the C4 position of the substrate, the conformation of which is equatorial in glucose-containing substrates and axial in galactose-containing substrates.
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