VP4

VP4 is a structural protein of rotaviruses, non-enveloped double-stranded RNA viruses in the family Reoviridae. It is encoded by genome segment 4 and forms part of the outer capsid, together with the VP7 glycoprotein. In many strains, VP4 is synthesized as a single precursor that is proteolytically cleaved upon maturation by host proteases, such as trypsin, into two subunits, VP8 and VP5. The VP8 moiety forms the distal spike that engages cell surface receptors, whereas VP5 contributes to membrane penetration during entry. The cleavage enhances infectivity in some host environments, and the conformation of the VP4 spike influences cell tropism and antigenicity.

Genetics and serotyping: The VP4 gene defines the P type of a rotavirus; combined with the VP7-defined G type, it determines the GxP[y] genotype that is used in surveillance. Numerous P-types exist; P[4], P[6], and P[8] are among the most globally encountered. VP4 sequence diversity drives antigenic variation and can affect neutralization by antibodies.

Clinical and research relevance: VP4 is a major target of neutralizing antibodies and is relevant to vaccine design and efficacy. Vaccines against rotavirus induce immune responses against multiple structural proteins including VP4; surveillance of VP4 types helps track circulating strains and inform vaccine composition. Methods for VP4 typing include RT-PCR and sequencing of segment 4.