PERTURBATION OF CONFORMATIONAL DYNAMICS, ENZYMATIC-ACTIVITY, AND THERMOSTABILITY OF BETA-GLYCOSIDASE FROM ARCHAEON SULFOLOBUS-SOLFATARICUS BY PH AND SODIUM DODECYL-SULFATE DETERGENT

The conformational dynamics of beta-glycosidase from Sulfolobus solfat aricus was investigated by following the emission decay arising from t he large number of tryptophanyl residues that are homogeneously disper sed in the primary structure, The fluorescence emission is characteriz ed by a bimodal lifetime distribution, suggesting that the enzyme stru cture contains rigid and flexible regions, properly located in the mac romolecule. The enzyme activity and thermostability appear to be relat ed to the dynamic properties of these regions as evidenced by perturba tion studies of the enzyme structure at alkaline pH and by addition of detergents such as SDS, The pH increase affects the protein dynamics with a remarkable loss of thermal stability and activity; these change s occur without any significant variation in the secondary structure a s revealed by far-UV dichroic measurements, In the presence of 0.02% ( w/v) SDS at alkaline pH, the enzymatic activity and thermostability ar e recovered, Under these conditions, the conformational dynamics appea r to be similar to that evidenced at neutral pH. Further increases in SDS concentration, at alkaline pH, render the activity and thermostabi lity of beta-glycosidase similar to those observed in the absence of d etergent, Proteins 27:71-79 (C) 1997 Wiley-Liss, Inc.