DIFFERENTIAL STABILITY OF BETA-SHEETS AND ALPHA-HELICES IN BETA-LACTAMASE - A HIGH-TEMPERATURE MOLECULAR-DYNAMICS STUDY OF UNFOLDING INTERMEDIATES

Beta-Lactamase, which catalyzes beta-lactam antibiotics, is prototypic al of large alpha/beta proteins with a scaffolding formed by strong no ncovalent interactions. Experimentally, the enzyme is well characteriz ed, and intermediates that are slightly less compact and having nearly the same content of secondary structure have been identified in the f olding pathway. In the present study, high temperature molecular dynam ics simulations have been carried out on the native enzyme in solution . Analysis of these results in terms of root mean square fluctuations in cartesian and [phi, psi] space, backbone dihedral angles and second ary structural hydrogen bonds forms the basis for an investigation of the topology of partially unfolded states of beta-lactamase. A differe ntial stability has been observed for alpha-helices and beta-sheets up on thermal denaturation to putative unfolding intermediates. These obs ervations contribute to an understanding of the folding/unfolding proc esses of beta-lactamases in particular, and other alpha/beta proteins in general.