The beta-glycosidase from the hyperthermophilic archaeon Sulfolobus solfataricus: enzyme activity and conformational dynamics at temperatures above 100 degrees C

Enzymes from thermophilic organisms are stable and active at temperatures w hich rapidly denature mesophilic proteins. However, there is not yet a comp lete understanding of the structural basis of their thermostability and the rmoactivity since for each protein there seems to exist special networks of interactions that make it stable under the desired conditions. Here we hav e investigated the activity and conformational dynamics above 100 degrees C of the beta-glycosidase isolated from the hyperthermophilic archaeon Sulfo lobus solfataricus. This has been made possible using a special stainless s teel optical pressure cell which allowed us to perform enzyme assays and fl uorescence measurements up to 160 degrees C without boiling the sample. The beta-glycosidase from S. solfataricus showed maximal activity at 125 degre es C. The time-resolved fluorescence studies showed that the intrinsic tryp tophanyl fluorescence emission of the protein was represented by a bimodal distribution with Lorential shape and that temperature strongly affected th e protein conformational dynamics. Remarkably, the tryptophan emission reve als that the indolic residues remain shielded from the solvent even at 125 degrees C, as shown by shielding from quenching and restricted tryptophan s olubility. The relationship between enzyme activity and protein structural dynamics is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.