Tap

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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History
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transporter associated with antigen processing; ATP-binding cassette, sub-family B; antigen peptide transporter

Definition
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TAP stands for the acronym "transporter associated with antigen processing" a heterodimeric transporter protein complex. The antigen peptide transporter consists of two proteins encoded by the TAP1 and TAP2 genes, respectively, located on the short arm of chromosome 6 p21.3. TAP is located in the membrane of the endoplasmic reticulum (ER) and is found in animals and fungi.

TAP catalyzes the import of peptides from the cytosol into the endoplasmic reticulum (ER) during antigen presentation. TAP is a transport protein from the family of so-called ABC transporters.

Structurally, the TAP protein forms a heterodimer consisting of a transmembrane domain and a nucleotide binding domain. During antigen presentation (see below antigen presenting cell), as soon as an antigen is introduced into the ER by TAP, the peptide is incorporated into the peptide-binding pocket of the MHC class I complex (if the peptide fits structurally into this pocket). The peptide-loaded TAP joins with the newly synthesised MHC molecules and 4 chaperones to form the peptide loading complex (PLC = peptide loading complex) and can then be further processed.

The ATPase activity of TAP is highly dependent on the presence of a correct substrate. This specificity is a very important barrier that prevents the unchecked activation of this enzyme complex.

Mutations in the TAP1 or TAP2 gene can lead to various diseases, including immune system disorders.

Literature
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  1. Abele R et al.(2004) The ABCs of immunology: structure and function of TAP, the transporter associatedwith antigen processing. Physiology (Bethesda) 19:216-224.
  2. El Hage F et al.(2013) TAP expression level in tumor cells defines the nature and processing of MHC class I peptides for recognition by tumor-specific cytotoxic T lymphocytes. Ann N Y Acad Sci 1283:75-80.

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Antigen; Antigen presentation;

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Last updated on: 29.10.2020