Xylanase from the psychrophilic yeast Cryptococcus adeliae

A xylanase belonging to family 10 is produced by Cryptococcus adeliae, an A ntarctic yeast that exhibits optimal growth at low temperature, The mature glycosylated xylanase secreted by C. adeliae is composed of 338 amino acid residues and 26 +/- 3 osidic residues, and shares 84% identity with its mes ophilic counterpart from C. albidus. The xylanase from C. adeliae is less t hermostable than its mesophilic homologue when the residual activities are compared, and this difference was confirmed by differential scanning calori metry experiments. In the range 0 degrees-20 degrees C, the cold-adapted xy lanase displays a lower activation energy and a higher catalytic efficiency . All these observations suggest a less compact, more flexible molecular st ructure. Analysis of computerized molecular models built up for both psychr ophilic and mesophilic xylanases indicates that the adaptation to cold cons ists of discrete changes in the tridimensional structure: of 53 substitutio ns, 22 are presumably involved in the adaptation process. These changes lea d mainly to a less compact hydrophobic packing, to the loss of one salt bri dge, and to a destabilization of the macrodipoles of the helices.