Figure 1. Schematic structures of viral host cell receptors. CAR is a receptor for coxsackie B viruses and adenoviruses, CD155 is a poliovirus receptor, CD4 is recognized by Human immunodeficiency virus (HIV), whereas intercellular adhesion molecule (ICAM)-1 acts as a receptor for most rhinoviruses. These four molecules are members of the immunoglobulin (Ig) superfamily containing typical immunoglobulin-like domain structures. Integrins are dimers that consist of and subunits. Integrins mediate cell–cell and cell–matrix interactions, and they are cellular receptors for members of several virus groups including adenoviruses, hantaviruses and picornaviruses. DAF (decay-accelerating factor; CD55) is a glycosylphosphatidylinositol-anchored complement regulatory protein that plays a role in the initiation of echovirus infection. Chemokine receptors are utilized by HIV during its entry into host cells.

Figure 2. Examples of virus–receptor interactions. (a) Cross-section of part of the human rhinovirus capsid shows a depression surrounding the 5-fold axis (top of figure) with a narrow channel structure in the middle. The terminal immunoglobulin (Ig)-like domain (D1) of intercellular adhesion molecule (ICAM)-1 binds to the outer wall of the depression and mediates virus–cell interactions that lead to attachment, entry and uncoating of the virus. These events can be blocked by drugs that attach to the pocket structure under the bottom of the depression. (b) Human immunodeficiency virus (HIV) recognizes primarily the CD4 molecule on the cell surface. As a consequence of this interaction, the external part (gp120) of the viral membrane protein undergoes structural changes that allow its binding to the chemokine receptors. Subsequently, the fusion peptide is exposed in the transmembrane protein gp41, and it causes the fusion of viral and cellular membranes that is followed by internalization of the capsid of the virus particle.