Transporter associated with antigen processing - wikipedia Transporter associated with antigen processing transporter 1, ATP - binding cassette, sub-family B ( MDR / TAP ) Identifiers Symbol TAP1 Alt. symbols ABCB2 Entrez 6890 HUGO 43 OMIM 170260 RefSeq NM_000593 UniProt Q03518 Other data Locus Chr. 6 p21. 3 transporter 2, ATP - binding cassette, sub-family B ( MDR / TAP ) Identifiers Symbol TAP2 Alt. symbols ABCB3 Entrez 6891 HUGO 44 OMIM 170261 RefSeq NM_000544 UniProt Q03519 Other data Locus Chr. 6 p21. 3 Transporter associated with antigen processing ( TAP ) is a member of the ATP - binding - cassette transporter family. It delivers cytosolic peptides into the endoplasmic reticulum ( ER ), where they bind to nascent MHC class I molecules. The TAP structure is formed of two proteins : TAP - 1 and TAP - 2, which have one hydrophobic region and one ATP - binding region each. They assemble into a heterodimer, which results in a four - domain transporter. Contents 1 Function 1.1 Peptide transport 1.2 Specificity 2 See also 3 References 4 External links Function The TAP transporter is found in the ER lumen associated with the peptide - loading complex ( PLC ). This complex of β2 microglobulin, calreticulin, ERp57, TAP, tapasin, and MHC class I acts to keep hold of MHC molecules until they have been fully loaded with peptides. Peptide transport TAP - mediated peptide transport is a multistep process. The peptide - binding pocket is formed by TAP - 1 and TAP - 2. Association with TAP is an ATP - independent event, ' in a fast bimolecular association step, peptide binds to TAP, followed by a slow isomerisation of the TAP complex '. It is suggested that the conformational change in structure triggers ATP hydrolysis and so initiates peptide transport. Both nucleotide - binding domains ( NBDs ) are required for peptide translocation, as each NBD can not hydrolyse ATP alone. The exact mechanism of transport is not known ; however, findings indicate that ATP binding to TAP - 1 is the initial step in the transport process, and that ATP bound to TAP - 1 induces ATP binding in TAP - 2. It has also been shown that undocking of the loaded MHC class I is linked to the transport cycle of TAP caused by signals from the TAP - 1 subunit. Specificity The ATPase activity of TAP is highly dependent on the presence of the correct substrate, and peptide binding is prerequisite for ATP hydrolysis. This prevents waste of ATP via peptide - independent hydrolysis. The specificity of TAP proteins was first investigated by trapping peptides in the ER using glycosylation. TAP binds to 8 - to 16 - residue peptides with equal affinity, while translocation is most efficient for peptides that are 8 to 12 residues long. Efficiency reduces for peptides longer than 12 residues. However, peptides with more than 40 residues were translocated, albeit with low efficiency. Peptides with low affinity for the MHC class I molecule are transported out of the ER by an efficient ATP - dependent export protein. These outlined mechanisms may represent a mechanism for ensuring that only high - affinity peptides are bound to MHC class I. See also Endoplasmic Reticulum MHC Class I Immune System References Jump up ^ Daumke O, Knittler MR ( 2001 ). `` Functional asymmetry of the ATP - binding - cassettes of the ABC transporter TAP is determined by intrinsic properties of the nucleotide binding domains ''. Eur. J. Biochem. 268 ( 17 ) : 4776 -- 86. doi : 10.1046 / j. 1432 - 1327.2001. 02406. x. PMID 11532014. Jump up ^ Suh WK, Cohen - Doyle MF, Fruh K, Wang K, Peterson PA, Williams DB ( 1994 ). `` Interaction of MHC class I molecules with the transporter associated with antigen processing ''. Science. 264 ( 5163 ) : 1322 -- 6. doi : 10.1126 / science. 8191286. PMID 8191286. Jump up ^ Janeway CA, Travers P, Walport M, Shlomchik M ( 2001 ). `` Chapter 5, Antigen Presentation to T - lymphocytes ''. In Janeway, Charles. Immunobiology : the immune system in health and disease ( 5th ed. ). New York : Garland. ISBN 0 - 8153 - 3642 - X. Jump up ^ Antoniou AN, Powis SJ, Elliott T ( 2003 ). `` Assembly and export of MHC class I peptide ligands ''. Curr. Opin. Immunol. 15 ( 1 ) : 75 -- 81. doi : 10.1016 / S0952 - 7915 ( 02 ) 00010 - 9. PMID 12495737. Jump up ^ van Endert PM, Tampé R, Meyer TH, Tisch R, Bach JF, McDevitt HO ( 1994 ). `` A sequential model for peptide binding and transport by the transporters associated with antigen processing ''. Immunity. 1 ( 6 ) : 491 -- 500. doi : 10.1016 / 1074 - 7613 ( 94 ) 90091 - 4. PMID 7895159. ^ Jump up to : Neumann L, Tampé R ( 1999 ). `` Kinetic analysis of peptide binding to the TAP transport complex : evidence for structural rearrangements induced by substrate binding ''. J. Mol. Biol. 294 ( 5 ) : 1203 -- 13. doi : 10.1006 / jmbi. 1999.3329. PMID 10600378. Jump up ^ Alberts P, Daumke O, Deverson EV, Howard JC, Knittler MR ( 2001 ). `` Distinct functional properties of the TAP subunits coordinate the nucleotide - dependent transport cycle ''. Curr. Biol. 11 ( 4 ) : 242 -- 51. doi : 10.1016 / S0960 - 9822 ( 01 ) 00073 - 2. PMID 11250152. Jump up ^ Neefjes JJ, Momburg F, Hämmerling GJ ( 1993 ). `` Selective and ATP - dependent translocation of peptides by the MHC - encoded transporter ''. Science. 261 ( 5122 ) : 769 -- 71. doi : 10.1126 / science. 8342042. PMID 8342042. Jump up ^ Lankat - Buttgereit B, Tampé R ( 2002 ). `` The transporter associated with antigen processing : function and implications in human diseases ''. Physiol. Rev. 82 ( 1 ) : 187 -- 204. doi : 10.1152 / physrev. 00025.2001. PMID 11773612. External links transporter associated with antigen processing ( TAP ) at the US National Library of Medicine Medical Subject Headings ( MeSH ) Membrane proteins, carrier proteins : membrane transport proteins ABC - transporter ( TC 3A1 ) A1 A2 A3 A4 A7 A8 A12 A13 B1 B2 - 3 ( B2 B3 ) B4 B5 B6 B7 B9 B11 C1 C2 C3 C4 C5 C6 C7 C8 - 9 ( C8, C9 ) C10 C11 C13 D1 D2 D3 D4 E1 F1 F2 G1 G2 G4 Sterolin ( G5, G8 ) see also ABC transporter disorders Retrieved from `` https://en.wikipedia.org/w/index.php?title=Transporter_associated_with_antigen_processing&oldid=724015934 '' Categories : Genes on human chromosome 6 ABC transporters Immune system Hidden categories : Protein pages needing a picture Talk Contents About Wikipedia Deutsch Italiano Edit links This page was last edited on 6 June 2016, at 16 : 53. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. 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Question: transport of peptides from the cytosol into the endoplasmic reticulum is via
Answer: Transporter associated with antigen processing (TAP)