VP4 spike-like protein of rotavirus
Viruses are parasites that use the host cell machinery to replicate and spread. Their genetic material is either in the form of RNA or DNA and is covered by a protective coat called the capsid. Some viruses, called enveloped viruses, also have a lipid bilayer membrane that encloses the capsid. Enveloped virsuses can leave the host cell by budding from its cell membrane while non-enveloped virsuses spread from the host cells by causing its lysis or bursting. Viruses use the transcription and translation machinery of the host cell to replicate their genome and synthesize proteins required for the formation of capsids and other proteins that it requires to get out of the host cell and infect other surrounding cells. All virus genomes encode three kinds of proteins-those that help replicate the genome, those that package the genome and deliver it to more host cells, and those that alter the structure or function of the host cell to suit the needs of the virus. Rotavirus is a non-enveloped virus i.e. one without a lipid-bilayer membrane, which causes gastroenteritis. The virus uses a spike protein, Vp4, to breach the target host cell membrane and enter the cytoplasm. The entry of the virus into the host cell is triggered by a structural rearrangement of Vp4 caused by trypsin cleavage.
The structure here is that of the part of the Vp4 protein that projects from the virion (a single virus particle) after trypsin cleavage. The structure is an umbrella-shaped homotrimer. Each monomer has a C-terminal alpha-helical, a triple coiled-coil which forms the post of the umbrella, and an N-terminal globular domain which forms the top of the umbrella. It is possible that this rigidified structure with its hydrophobic apex penetrates the host cell membrane to allow the virus to enter the cytoplasm.
Protein Data Bank (PDB)
Dormitzer, P.R. Nason, E.B. Prasad, B.V.V. Harrison, S.C.; "Structural rearrangements in the membrane penetration protein of a non-enveloped virus."; Nature; (2004) 430:1053-1058. PubMed:15329727
Author: Ashwini Patil