National Research Council of Canada

David R Rose

Warren W Wakarchuk

Wing L Sung

Makoto Yaguchi

Robert L Campbell

The thermostability of the 20,396 dalton Bacillus circulans xylanase was increased by site-directed mutagenesis. The thermostability was conferred by the presence of non-native disulfide bridges, and selected N-terminal mutations. The introduction of these non-native disulfide bridges was accomplished by the examination of the three-dimensional structure of the enzyme, and choosing sites where a favorable geometry for a bridge existed. The N-terminal mutations were constructed on the basis of primary sequence comparison with other family G xylanases. The mutant proteins were examined for their ability to retain enzymatic activity after heating as an indication of increased thermostability. These thermotolerant variants are useful as an alternative to chemical bleaching of Kraft pulp in a pre-bleaching step (bio-bleaching). The pre-bleaching involves temperatures higher than that normally used for these enzymes and accordingly these thermotolerant variants can be advantageously used at this step. Thermotolerant xylanases are also of use in the food processing industry.

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Markham, Canada

David R Rose