Crystal structure of the beta-glycosidase from the hyperthermophile Thermosphaera aggregans: insights into its activity and thermostability

The glycosyl hydrolases are an important group of enzymes that are responsi ble for cleaving a range of biologically significant carbohydrate compounds . Structural information on these enzymes has provided useful information o n their molecular basis for the functional variations, while the characteri zation of the structural features that account for the high thermostability of proteins is of great scientific and biotechnological interest. To these ends we have determined the crystal structure of the beta-glycosidase from a hyperthermophilic archeon Thermosphaera a aggregans. The structure is a (beta/alpha)(8) barrel (TIM-barrel), as seen in other glycosyl hydrolase fa mily 1 members, and forms a tetramer. Inspection of the active site and the surrounding area reveals two catalytic glutamate residues consistent with the retaining mechanism and the surrounding polar and aromatic residues con sistent with a monosaccharide binding site. Comparison of this structure wi th its mesophilic counterparts implicates a variety of structural features that could contribute to the thermostability. These include an increased nu mber of surface ion pairs, an increased number of internal water molecules and a decreased surface area upon forming an oligomeric quaternary structur e. (C) 1999 Federation of European Biochemical Societies.