The interaction of the non-enveloped plant viruses TMV (rod-shaped) and CCMV (spherical) and of their coat
proteins in several well-defined aggregation states, with
artificial membranes was investigated to study the early stages of the cellular
infection process. Information about the separate steps in the interaction mechanisms was obtained by employing three assays, performed as a function of vesicle size, net membrane charge, pH and ionic strength. The assays allow to discriminate between aggregation of vesicles (turbidity assay) and membrane destabilization (vesicle leakage assay and
lipid mixing assay). The aggregation of the vesicles is a result of electrostatic interactions between the viral material and vesicles surface (cross-linking), while the destabilization of the membrane is a result of penetration or bilayer disruption by hydrophobic protein domains. TMV virions and its coat
protein, and CCMV virions, due to their net negative charge, predominantly interact with positively charged membranes. The coat
protein of CCMV was found to interact with negatively charged membranes, an interaction that can be assigned to its basical N-terminal sequence. Changing the aggregational state of the
viral coat proteins yielded most significant interactions in case of TMV coat
protein aggregated in the disk form and CCMV coat
protein aggregated in empty capsids with oppositely charged membranes. These
protein aggregates are found to be the best compromise between efficiency (capacity of the
protein to bridge vesicles and destabilize their membranes) and concentration of
protein aggregates. The results are discussed with respect to previously proposed
biological models of the early stages of plant virus
infection.