A highly membrane-active peptide in Flock House virus: implications for the mechanism of nodavirus infection Original Research Article

Background Nodaviruses are among the simplest animal viruses, and are therefore attractive systems for deconvoluting core viral processes such as assembly, infection and uncoating. Membrane translocation of the single-stranded RNA genome of nodaviruses has been proposed to be mediated by direct lipid-protein interactions between a post-assembly autocatalytic cleavage product from the capsomere and the target membrane. To probe the validity of this hypothesis, we have synthesized a 21-residue Met→Nle (norleucine) variant of the amino-terminal helical domain (denoted here as γ1) of the cleavage peptide in Rock House nodavirus (FHV) and studied its ability to alter membrane structure and function. Results The synthetic peptide γ1 increases membrane permeability to hydrophilic solutes, as judged by fluorescence experiments with liposomeencapsulated dyes and ion-conductance measurements. Furthermore, peptide orientation and location within lipid bilayers was determined using tryptophan-fluorescence-quenching experiments and attenuated total reflectance infrared spectroscopy. Conclusions The helical domain of the FHV cleavage product partitions spontaneously into lipid bilayers and increases membrane permeability, consistent with the postulated mechanism for viral genome translocation. The existence of a membrane-binding domain in the FHV cleavage sequence suggests peptide-triggered disruption of the endosomal membrane as a prelude to viral uncoating in the host cytoplasm. A model for this interaction is proposed.