CONFORMATIONAL-CHANGES IN AEROLYSIN DURING THE TRANSITION FROM THE WATER-SOLUBLE PROTOXIN TO THE MEMBRANE CHANNEL

Proteolytic activation, oligomerization, and membrane insertion are th ree steps that precede channel formation by the bacterial toxin aeroly sin. Using attenuated total reflection Fourier transform infrared spec troscopy (ATR-FTIR) and hydrogen-deuterium exchange, the structural ch anges associated with each step were analyzed. Our results show that a ctivation induces a significant change in secondary structure, charact erized by a decrease in random structure and an increase in beta-sheet content, We show that release of the propeptide is essential for this conformational change to occur and that changes are not restricted to the vicinity of the cleavage site but appear to propagate along the m olecule. In contrast, subsequent oligomerization of the mature toxin d oes not involve any change in overall secondary structure bur does inv olve a modification of the tertiary interactions, Finally, insertion o f the heptameric complex into dimyristoylphosphatidylcholine vesicles also occurs without major modification of the secondary structure, Stu dies on the orientations of tile secondary structures of the heptamer in the lipid bilayer have also been performed.