Novel immunological reagents against minor receptor group human rhinovirus

Rhinoviruses are the main causative agents of common cold infections. Due to the large number of different virus strains, more than 100 have been detected, vaccination is not feasible. In order to intervene at the very first event in infection, the attachment of the virus to the cell surface, a better understanding of the type of interaction of the components is necessary. We therefore produced segments of the viral receptor, the protein which the minor group of these viruses binds to at the cell surface, by gene technological methods. As these fragments lack the region which anchors the natural receptor in the cell membrane they are soluble. It was found that the larger versions of these recombinant fragments were able to neutralize all 10 virus strains belonging to the minor rhinovirus group. This demonstrates that they indeed attach to the site also recognized by the cellular receptor. In an attempt to further characterize the virus - receptor interaction, fragments were produced which bind to the virus in a defined way and remain stably associated. Complexes between virus and receptor fragments were then analyzed by cryo-electron microscopy in collaboration with E. Hewat`s group in Grenoble. For this method, the material is quickly frozen to be trapped in a native form in amorphous ice. Images are then submitted to mathematical analysis resulting in three-dimensional models at about 2nm resolution. The images showed that the receptor molecules attach to the star-shaped dome at the five-fold axis of the icosahedral virion. This is remarkable since the receptor of major group viruses was previously shown to attach in the canyon, a cleft encircling the five-fold symmetry axes but is remote of the star shaped dome. Determination of the binding site of a minor group rhinovirus receptor paves the way to identify amino acid residues involved in the interaction. Furthermore, comparison of the amino acid sequence of all 10 minor group rhinoviruses will reveal the basis of receptor discrimination and eventually suggest means of more efficiently inhibiting viral infection by preventing the virus from attaching to the host cell.