Identification of domain boundaries within the N-termini of TAP1 and TAP2 and their importance in tapasin binding and tapasin-mediated increase in peptide loading of MHC class I

Erik Procko, Gayatri Raghuraman, Don C. Wiley, Malini Raghavan, Rachelle Gaudet

Research output: Contribution to journalArticle

Abstract

Before exit from the endoplasmic reticulum (ER), MHC class I molecules transiently associate with the transporter associated with antigen processing (TAP1/TAP2) in an interaction that is bridged by tapasin. TAP1 and TAP2 belong to the ATP-binding cassette (ABC) transporter family, and are necessary and sufficient for peptide translocation across the ER membrane during loading of MHC class I molecules. Most ABC transporters comprise a transmembrane region with six membrane-spanning helices. TAP1 and TAP2, however, contain additional N-terminal sequences whose functions may be linked to interactions with tapasin and MHC class I molecules. Upon expression and purification of human TAP1/TAP2 complexes from insect cells, proteolytic fragments were identified that result from cleavage at residues 131 and 88 of TAP1 and TAP2, respectively. N-Terminally truncated TAP variants lacking these segments retained the ability to bind peptide and nucleotide substrates at a level comparable to that of wild-type TAP. The truncated constructs were also capable of peptide translocation in vitro, although with reduced efficiency. In an insect cell-based assay that reconstituted the class I loading pathway, the truncated TAP variants promoted HLA-B*2705 processing to similar levels as wild-type TAP. However, correlating with the observed reduction in tapasin binding, the tapasin-mediated increase in processing of HLA-B*2705 and HLA-B*4402 was lower for the truncated TAP constructs relative to the wild type. Together, these studies indicate that N-terminal domains of TAP1 and TAP2 are important for tapasin binding and for optimal peptide loading onto MHC class I molecules.

Original languageEnglish (US)
Pages (from-to)475-482
Number of pages8
JournalImmunology and Cell Biology
Volume83
Issue number5
DOIs
StatePublished - Oct 2005

Keywords

  • ATP-binding cassette (ABC) transporter
  • Antigen presentation
  • Tapasin
  • Transporter associated with antigen processing (TAP)

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology
  • Cell Biology

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