THE 3-DIMENSIONAL STRUCTURE OF TRYPSIN-TREATED STAPHYLOCOCCUS-AUREUS ALPHA-TOXIN

Trypsin treatment of staphylococcal α-toxin cleaves the molecule into two roughly equally sized parts, which ] results in inactivation of the toxin. Tetragonal arrays of oligomers, closely resembling the native ones, can however be formed on lipid layers. From tilted views of negatively stained crystals a 31) structure to 23 Å resolution has been determined by electron microscopy and image processing. On comparison with the 31) structure of the native ot-toxin (Olofsson et al., J. Mol. Biol. 214, 299-306, 1990) the subdomains are more separated, confirming the differences found when comparing the projection maps (Olofsson et al., J. Struct. Biol. 106, 199-204, 1991). The tryptic cleavage takes place in a postulated hinge region. The results are consistent with the hypothesis that the conformational change required for inducing the membrane permeabilizing property takes place in this region. Furthermore, we present a refined projection map at approximately 10 Å resolution based on the analysis of a large number of crystals using unbending methods. © 1992.