♦Outer capsid protein VP4 (Hemagglutinin) [Cleaved into: Outer capsid protein VP8*
♦ Outer capsid protein VP5*]

NC_011500.2 ;  NC_011501.2 ;  NC_011502.2 ;  NC_011503.2 ;  NC_011504.2 ;  NC_011505.2 ;  NC_011506.2 ;  
NC_011507.2 ;  NC_011508.2 ;  NC_011509.2 ;  NC_011510.2 ;  NC_011511.2 

MASLIYRQLLSNSYVTNISDEVSEIGARKTANVTVNPGPFAQTGYAPVNWGHGELSDSTLVQPTLDGPYQPTTFNLPIDYWMLIAPTQIGRVAEGTNTTN
RWFACVLVELNVQNTQREYVLDGQTVQLQVSNDSSTLWKFILFIKLEKNGTYTQYSTLSTSNKLCAWMKREGRVYSYAGVTPNASESYYLTINNDDSNVS
SDAEFYLIPQSQTELCTQYINNGLPPIQNTRNVVPVSLTSREIRHSRAQMNEDIVVSKTSLWKEMQYNRDITIRFKFANSIVKSGGLGYKWSEISFKPMN
YQYTYTRDGEEITAHTTCSVNGVNDFTYNGGPLPTDFAISRFEVIKENSYVYIDYWDDSQAFRNMVYVRSLAADLNDVVCSGGDYSFALPVGAYPIMSGG
AVTLSPAGVTLSTQFTDYVSLNSLRFRFRLAVSEPSFSISRTRLSGIYGLPAANPNNSVEYYEIAGRFSLISLVPTNDDYQTPIANSVTVRQDLERQLGE
LREEFNSLSQEIALSQLIDLATLPLDMFSMFSGIKSTVEAVKSMTTNIMKKFKTSNLANAISDLTNSMSDAASSISRSASVRSIGSNTTMRISTAIQTGE
DLRTMTDASTQISNVSRSLRLREFTTQTDNLSFDDISAAVLKTKLDKSTQISQTTIPDIISESSEKFIPMRTYRVMDNDTGFETGIDGTFYAYRIDTFDE
IPFDVEKFNRLITDSPVLSAIIDFKTLKNLNDNYGITKTQAMELLQSNPRTLKEFINSNNPIIRNRIENLIAQCRL

♦Outer capsid protein VP4: 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 attachment and entry into the host cell probably involves multiple sequential contacts between the outer capsid proteins VP4 and VP7, and the cell receptors. It is subsequently lost, together with VP7, following virus entry into the host cell. Following entry into the host cell, low intracellular or intravesicular Ca(2+) concentration probably causes the calcium-stabilized VP7 trimers to dissociate from the virion. This step is probably necessary for the membrane-disrupting entry step and the release of VP4, which is locked onto the virion by VP7. During the virus exit from the host cell, VP4 seems to be required to target the newly formed virions to the host cell lipid rafts.
♦ Outer capsid protein VP5*: Forms the spike "foot" and "body" and acts as a membrane permeabilization protein that mediates release of viral particles from endosomal compartments into the cytoplasm. During entry, the part of VP5* that protrudes from the virus folds back on itself and reorganizes from a local dimer to a trimer. This reorganization may be linked to membrane penetration by exposing VP5* hydrophobic region. In integrin-dependent strains, VP5* targets the integrin heterodimer ITGA2/ITGB1 for cell attachment.
♦ Outer capsid protein VP8*: Forms the head of the spikes and mediates the recognition of specific host cell surface glycans. 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. In some other strains, VP8* mediates the attachment to histo-blood group antigens (HBGAs) for viral entry.

♦ Outer capsid protein VP4: Virion . Host rough endoplasmic reticulum . Host cell membrane . Host cytoplasm, host cytoskeleton . Host endoplasmic reticulum-Golgi intermediate compartment . Note=The outer layer contains 180 copies of VP4, grouped as 60 dimers. 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. VP4 also seems to associates with lipid rafts of the host cell membrane probably for the exit of the virus from the infected cell by an alternate pathway. .
♦ Outer capsid protein VP8*: Virion . Note=Outer capsid protein. .
♦ Outer capsid protein VP5*: Virion . Note=Outer capsid protein. .

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