Infrared spectroscopy study on the conformational changes leading to pore formation of the toxin Sticholysin II

Abstract

The structure of the actinoporin sticholysin II (StnII) in the pore state was investigated by Fourier transform infrared
spectroscopy in the attenuated total reflection configuration. 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/cholesterol unilamellar
vesicles were employed. The a-helix content increases in;30% upon lipid binding, which agrees with an extension of eight
or nine residues at the N-terminal helix. Furthermore, analyses of dichroic spectra show that the extended N-terminal helix would
have a 31º tilt with respect to the membrane normal. The orientation of the central beta-sandwich was also estimated. In addition, it was
detected that StnII alters the orientation of the lipid acyl chains. 1H/2Hexchange experiments sustain a mainly superficial interaction
between StnII and the membrane, with no protection of the beta-sandwich. The implications of the results in the mechanism of pore
formation are discussed.