thumb|Diagram of how a virus capsid can be constructed using multiple copies of just two protein molecules

The term viral protein refers to both the products of the genome of a virus and any host proteins incorporated into the viral particle. Viral proteins are grouped according to their functions, and groups of viral proteins include structural proteins, nonstructural proteins, regulatory proteins, and accessory proteins. Viruses are non-living and do not have the means to reproduce on their own, instead depending on their host cell's machinery to do this. Thus, viruses do not code for most of the proteins required for their replication and the translation of their mRNA into viral proteins, but use proteins encoded by the host cell for this purpose.

Viral structural proteins

Most viral structural proteins are components for the capsid and the envelope of the virus.

Capsid

The genetic material of a virus is stored within a viral protein structure called the capsid. The capsid is a "shield" that protects the viral nucleic acids from getting degraded by host enzymes or other types of pesticides or pestilences. It also functions to attach the virion to its host, and enable the virion to penetrate the host cell membrane. Many copies of a single viral protein or a number of different viral proteins make up the capsid, and each of these viral proteins are coded for by one gene from the viral genome. The structure of the capsid allows the virus to use a small number of viral genes to make a large capsid.

Several protomers, oligomeric (viral) protein subunits, combine to form capsomeres, and capsomeres come together to form the capsid. The viral envelope is made up of a lipid bilayer embedded with viral proteins, including viral glycoproteins.

Viral membrane fusion proteins

The fusion of the viral envelope with the cellular membrane requires high energy to occur. Viral membrane fusion proteins act as catalysts to overcome this high energy barrier. Following viral glycoprotein binding to cellular receptors, viral membrane fusion proteins undergo a change in structure conformation. Other viral nonstructural proteins such as NS5A, NS5B, and NS3, are also recruited to the complex, and NS4B interacts with them and binds to viral RNA. Such proteins hold potential in developing new bio-pharmaceutical treatments for inflammatory disease in humans, as the proteins have been proven to subvert inflammatory immune mediators. Viral nonstructural protein NS1 in the West Nile virus prevents complement activation through its binding to a complement control protein, factor H.

Viral regulatory and accessory proteins

Viral regulatory and accessory proteins have many functions. These viral proteins control and influence viral gene expressions in the viral genome, including viral structural gene transcription rates.

Viral accessory proteins, also known as auxiliary proteins, are coded for by the genome of retroviruses. Most viral accessory proteins only carry out their functions in specific types of cells.

References

  • List of all known Viral Proteins in UniProtKB
  • VirusMint