The localization and function of the neutralizing protein, VP4, in human rotavirus

The binding sites of a monoclonal antibody (mAb) to human rotavirus VP4 (K-1532) on the virion surface were examined with electron microscopy and the Markham photorotation method. The mAb, which had both hemagglutination inhibiting and neutralizing activities, appeared to bind to the outer margin of double-shelled particles of human rotavirus, especially to the parts overlaying the tubelike channels, which seemed to be the "cover lid" of the tubelike channels that extruded radially from the core region. This binding point may be a putative fusion site of the virus (Mackow et al. 1988) as well as a viral nucleus component ejection gate (Suzuki et al. 1986). Rotavirus particles treated with the mAb were shown to be capable of binding to MA104 cells by ultra-thin section examination. These observations suggest that neutralization via VP4 is related to virus uncoating but not to attachment of rotavirus.