STRUCTURE OF THE AEROMONAS TOXIN PROAEROLYSIN IN ITS WATER-SOLUBLE AND MEMBRANE-CHANNEL STATES

AEROLYSIN is chiefly responsible for the pathogenicity of Aeromonas hy drophila, a bacterium associated with diarrhoeal diseases and deep wou nd infections1. Like many other microbial toxins, the protein changes in a multistep process from a completely water-soluble form to produce a transmembrane channel that destroys sensitive cells by breaking the ir permeability barriers2. Here we describe the structure of proaeroly sin determined by X-ray crystallography at 2.8 angstrom resolution. Th e protoxin (M(r) 52,000) adopts a novel protein fold. Images of an aer olysin oligomer derived from electron microscopy have assisted in cons tructing a model of the membrane channel and have led to the proposal of a scheme to account for insertion of the protein into lipid bilayer s to form ion channels.