Outer Capsid Protein VP4 Rotavirus A Recombinant Protein

Function: Spike-forming protein that mediates virion attachment to the host epithelial cell receptors and plays a major role in cell penetration, determination of host range restriction and virulence. Rotavirus entry into the host cell probably involves multiple sequential contacts between the outer capsid proteins VP4 and VP7, and the cell receptors. According to the considered strain, VP4 seems to essentially target sialic acid and/or the integrin heterodimer ITGA2/ITGB1

By similarity.Outer capsid protein VP5*: forms the spike "foot" and "body". Acts as a membrane permeabilization protein that mediates release of viral particles from endosomal compartments into the cytoplasm. In integrin-dependent strains, VP5* targets the integrin heterodimer ITGA2/ITGB1 for cell attachment

By similarity.VP8* forms the head of the spikes. It is the viral hemagglutinin and an important target of neutralizing antibodies. In sialic acid-dependent strains, VP8* binds to host cell sialic acid, most probably a ganglioside, providing the initial contact

By similarity.

Subunit structure: VP4 is a homotrimer

Potential. VP4 adopts a dimeric appearance above the capsid surface, while forming a trimeric base anchored inside the capsid layer. Only hints of the third molecule are observed above the capsid surface. It probably performs a series of molecular rearrangements during viral entry. Prior to trypsin cleavage, it is flexible. The priming trypsin cleavage triggers its rearrangement into rigid spikes with approximate two-fold symmetry of their protruding parts. After an unknown second triggering event, cleaved VP4 may undergo another rearrangement, in which two VP5* subunits fold back on themselves and join a third subunit to form a tightly associated trimer, shaped like a folded umbrella. VP5* is a homotrimer

Potential. The trimer is coiled-coil stabilized by its C-terminus, however, its N-terminus, known as antigen domain or "body", seems to be flexible allowing it to self-associate either as a dimer or a trimer. The two- to three-fold reorganization and fold-back of VP5* may be linked to membrane penetration, by exposing its hydrophobic region. Interacts with host ITGA2 (via ITAG2 I-domain); this interaction occurs when ITGA2 is part of the integrin heterodimer ITGA2/ITGB1. Interacts with host integrin heterodimer ITGA4/ITGB1 and ITGA4/ITGB7

By similarity.

Subcellular location: Outer capsid protein VP4: Virion

By similarity. Host rough endoplasmic reticulum

Potential. Note: Immature double-layered particles assembled in the cytoplasm bud across the membrane of the endoplasmic reticulum, acquiring during this process a transient lipid membrane that is modified with the ER resident viral glycoproteins NSP4 and VP7; these enveloped particles also contain VP4. As the particles move towards the interior of the ER cisternae, the transient lipid membrane and the non-structural protein NSP4 are lost, while the virus surface proteins VP4 and VP7 rearrange to form the outermost virus protein layer, yielding mature infectious triple-layered particles

By similarity.Outer capsid protein VP8*: Virion. Note: Outer capsid protein

By similarity.Outer capsid protein VP5*: Virion. Note: Outer capsid protein

By similarity.

Post-translational modification: Proteolytic cleavage by trypsin results in activation of VP4 functions and greatly increases infectivity. The penetration into the host cell is dependent on trypsin treatment of VP4. It produces two peptides, VP5* and VP8* that remain associated with the virion

By similarity.

Miscellaneous: In group A rotaviruses, VP4 defines the P serotype.This strain has been shown to be sialic acid-independent in cell culture conditions

By similarity.

Sequence similarities: Belongs to the rotavirus VP4 family.