An Animal Virus-Derived Peptide Switches Membrane Morphology:  Possible Relevance to Nodaviral Transfection Processes<sup>†</sup>

The N-terminal domain of the capsid protein cleavage product of the flock house virus (FHV) consists of 21 residues and forms an amphipathic α-helix, which is thought to play a crucial role in permeabilizing biological membranes for RNA translocation in the host cell. We have found that the Met → Nle variant of this domain (denoted here as γ<sub>1</sub>) efficiently induces the formation of the interdigitated gel phase (L<sub>β</sub>I) of 1,2-dipalmitoyl-<i>sn</i>-glycero-3-phosphatidylcholine (DPPC) bilayers. In situ scanning force microscopy of solid supported bilayers and fluorescence spectroscopy of peptide-treated DPPC vesicles provide evidence for the formation of acyl chain interdigitated lipid domains. It could be shown by fluorescence spectroscopy that the peptide inserts in the DPPC matrix above the main transition temperature of the lipid, while the formation of domains with decreased thickness occurs after the sample is cooled to 25 °C. The orientation and secondary structure of the peptide in lipid bilayers were investigated using attenuated total reflectance infrared (ATR-IR) and circular dichroism (CD) spectroscopy. These results enabled us to formulate a mechanistic model for the peptide-mediated induction of interdigitation in DPPC bilayers. Moreover, the membrane activity of γ<sub>1</sub> with gel phase lipids established in this study may have further implications for the infection strategy adopted by simple RNA viruses.