CRYSTAL-STRUCTURE OF THE BETA-GLYCOSIDASE FROM THE HYPERTHERMOPHILIC ARCHEON SULFOLOBUS-SOLFATARICUS - RESILIENCE AS A KEY FACTOR IN THERMOSTABILITY

Enzymes from hyperthermophilic organisms must operate at temperatures which rapidly denature proteins from mesophiles. The structural basis of this thermostability is still poorly understood. Towards a further understanding of hyperthermostability we have determined the crystal s tructure of the beta-glycosidase (dan GH-1A, family 1) from the hypert hermophilic archaeon Sulfolobus solfataricus at 2.6 Angstrom resolutio n. The enzyme is a tetramer with subunit molecular mass at 60 kDa, and crystallises with half of the tetramer in the asymmetric unit. The st ructure is a (beta alpha)(8) barrel, but with substantial elaborations between the beta-strands and alpha-helices in each repeat. nle active site occurs at the centre of the top face of the barrel and is connec ted to the surface by a radial channel which becomes a blind-ended tun nel in the tetramer, and probably acts as the binding site for extende d oligosaccharide substrates. Analysis of the structure reveals two fe atures which differ significantly from mesophile proteins; (1) an unus ually large proportion of surface ion-pairs involved in networks that cross-link sequentially separate structures on the protein surface, an d (2) an unusually large number of solvent molecules buried in hydroph ilic cavities between sequentially separate structures in the protein core. These factors suggest a model for hyperthermostability via resil ience rather than rigidity. (C) 1997 Academic Press Limited.