Binding and entry of animal viruses

Viruses are infectious agents capable of packaging and delivering nucleic acids and proteins to specific populations of cells. To initiate infection, viruses bind to sites, or receptors, on the cell surface and transfer their genome across the limiting membrane of the cell. The mechanisms underlying these events, and viral tropism for particular host cells, are becoming increasingly well understood. Several cell surface proteins have now been identified as viral receptors, and analyses of intact virus particles and sub-viral components are revealing the structures of the binding determinants on the viruses themselves. For many viruses, the events leading to penetration and delivery involve constitutive endocytic properties of the host cell, and the low pH environment in endocytic compartments is a crucial trigger in the penetration process. The knowledge of viral tropism, binding and entry suggests strategies which may be applied to the design of targeted therapeutic agents with appropriate specificities and effective delivery mechanisms.