Virus protein

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A virus protein (often abbreviated as VP ) is a protein that is encoded by the genome of a virus . It is either part of the virus particle itself or is only produced in the cell during virus replication or latency.

Differentiation according to function

Functionally, a distinction is made between structural proteins and non-structural proteins in virus proteins . Structural proteins are involved in the structure of the virion , for example in the capsid as penton or hexon proteins , the virus envelope or as tegument or matrix proteins . Not all proteins that can be detected on the virion are virus proteins, since cellular proteins can also be stored in the virus envelope or packaged inside the virus. However, these are not encoded in the virus genome. An example is the packaging of ribosomal proteins in arenaviruses or histones in Polyomaviridae . Non-structural proteins fulfill functional tasks during virus replication in the cell, for example viral polymerases , proteases , control proteins of replication or cellular gene expression and the like. a., or they are released from the infected cell as factors of immune evasion , such as the HBe antigen of the hepatitis B virus (HBV).

Virus protein nomenclature

The nomenclature of the virus proteins is not uniform and in some cases differs between different virus families. The structural proteins are usually named after their function in the virion, i.e. as C protein (core, capsid), M protein (matrix) or E protein (virus envelope ); If there are several proteins with the same function, they are differentiated by numbering (E1, E2, M1 etc.). In the case of picornaviruses , for example , the structural proteins are also referred to as VP (virus protein) and numbered accordingly (VP1, VP2). In retroviruses , there is the special designation gag for the capsid proteins, and env for the envelope proteins. For historical reasons, the structural proteins of HBV are called HBc-Ag (hepatitis B virus core antigen ) and HBs antigen (hepatitis B virus surface antigen).

The non-structural proteins are often abbreviated as NS with subsequent numbering (NS2, NS3a, etc.). Within some virus families, the names for individual NS proteins are fixed, so that numbering can be skipped for individual virus species that lack this individual protein compared to other species within the family. Picornaviruses and flaviviruses use this nomenclature according to protein function and not according to the sequence in each individual genome . In retroviruses there is the term pol for the viral polymerase, in HBV the HBe antigen (hepatitis B virus E antigen), but here it does not stand for envelope (virus envelope).

Irrespective of the designation as structural or non-structural protein, virus proteins are sometimes named with their biochemical characterization for historical reasons or because of an unknown function ( p for protein, gp for glycoprotein ). Numbers are added to this designation, but they do not indicate numbering, but correspond to the rounded whole number of the molecular mass in kDa of the protein, for example p24, gp33, etc. This designation goes back to the investigation and identification of virus proteins by means of gel electrophoresis , in which the approximate molecular mass can be determined.

literature

  • David M. Knipe, Peter M. Howley (eds.-in-chief): Fields' Virology . 5th edition, 2 volumes Philadelphia 2007, ISBN 0-7817-6060-7
  • Brian WJ Mahy and Marc H. van Regenmortel (eds.): Encyclopedia of Virology , 3rd Edition, San Diego 2008 (Volumes 1-5) ISBN 978-0-12-373935-3