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

Background: Nodaviruses are among the simplest animal viruses, and are ther efore attractive systems for deconvoluting core viral processes such as ass embly, infection and uncoating. Membrane translocation of the single-strand ed RNA genome of nodaviruses has been proposed to be mediated by direct lip id-protein interactions between a past-assembly autocatalytic cleavage prod uct from the capsomere and the target membrane. To probe the validity of th is hypothesis, we have synthesized a 21-residue Met-->Nle (norleucine) vari ant of the amino-terminal helical domain (denoted here as gamma(1)) of the cleavage peptide in Flock House nodavirus (FHV) and studied its ability to alter membrane structure and function. Results: The synthetic peptide gamma(1) increases membrane permeability to hydrophilic solutes, as judged by fluorescence experiments with liposome-en capsulated dyes and ion-conductance measurements. Furthermore, peptide orie ntation and location within lipid bilayers was determined using tryptophan- fluorescence-quenching experiments and attenuated total reflectance infrare d spectroscopy. Conclusions: The helical domain of the FHV cleavage product partitions spon taneously into lipid bilayers and increases membrane permeability, consiste nt with the postulated mechanism for viral genome translocation. The existe nce of a membrane-binding domain in the FHV cleavage sequence suggests pept ide-triggered disruption of the endosomal membrane as a prelude to viral un coating in the host cytoplasm, A model for this interaction is proposed.