Site-directed mutagenesis of a yeast gene for improvement of enzyme thermostability.

Abstract

Enzyme stability is one of the critical factors to construct an efficient biological conversion system. Xylitol dehydrogenase (XDH) from Pichia stipitis is one of the key enzymes for bio-ethanol fermentation system from xylose. Previously, we tried to improve thermostability of XDH by introduction of structural zinc into the enzyme and successfully obtained a mutant, named C4 mutant, with an increased unfolding temperature (J. Biol. Chem., 280:10340-10349, 2005). We focused on further improvement of the thermostability of XDH in this study and employed subsequent site directed mutagenesis in structural zinc binding region for stabilizing the structural zinc binding loop. Two variants (C4/F98R and C4/E101F) showed higher thermostability than C4 mutant judged by thermal inactivation of enzyme activity and thermal transition temperature.