SUBUNIT ORGANIZATION AND SYMMETRY OF PORE-FORMING, OLIGOMERIC PNEUMOLYSIN

We present a detailed analysis of the oligomeric subunit organisation of pneumolysin by the use of negative stain electron microscopy and im age processing to produce a projection density map. Analysis of the ro tational symmetry has revealed a large and variable subunit number, be tween 40-50. The projected subunit density by rotational averaging sho ws at least two distinct subunit domains at different radial positions , Side views of the rings reveal further details concerning the dimens ions of the oligomer in the membrane. On the basis of these observatio ns and our previous knowledge of the monomer domain structure rye prop ose that the 4-domain subunits are packed in a square planar arrangeme nt to form the pneumolysin oligomer.