Components of Non-enveloped Viruses which Recognize Receptors

Non-enveloped animal viruses, in most cases, have icosahedral symmetry. Therefore, they have at least 12 identical sites for interaction with receptors on host cells. The multiple subunit structure of the virion capsid leads not only to multivalent receptor bonding, but may also confer allosteric properties to the virion. In this chapter, we will discuss structural features of primarily two families of non-enveloped viruses. The native capsids of many picoraviruses undergo major conformational changes when disrupted and their individual subunit polypeptides cannot be isolated easily in their ‘native’ condition or assigned separate biological functions. Adenoviruses, in contrast, provide an example where isolated capsid subunits retain activity, and one of these, the fiber, has been identified as the virus attachment protein which recognizes cellular receptors, while other subunits have other biological functions. Other non-enveloped viruses will be discussed briefly in relationship to these two families.