Activity and stability of hyperthermophilic enzymes: a comparative study on two archaeal beta-glycosidases

S beta gly and CelB are well-studied hyperthermophilic glycosyl hydrolases, isolated from the Archaea Sulfolobus solfataricus and Pyrococcus furiosus, respectively. Previous studies revealed that the two enzymes are phylogene tically related; they are very active and stable at high temperatures, and their overall three-dimensional structure is very well conserved. To acquir e insight in the molecular determinants of thermostability and thermoactivi ty of these enzymes, we have performed a detailed comparison, under identic al conditions, of enzymological and biochemical parameters of S beta gly an d CelB, and we have probed the basis of their stability by perturbations in duced by temperature, pH, ionic strength, and detergents. The major result of the present study is that, although the two enzymes are remarkably simil ar with respect to kinetic parameters, substrate specificity, and reaction mechanism, they are strikingly different in stability to the different phys ical or chemical perturbations induced. These results provide useful inform ation for the design of further experiments aimed at understanding the stru cture-function relationships in these enzymes.