Hydrophobic Interactions Are Key To Drive the Association of Tapasin with Peptide Transporter Subunit TAP2

J Immunol. 2015 Dec 1;195(11):5482-94. doi: 10.4049/jimmunol.1500246. Epub 2015 Oct 30.

Abstract

The transporter associated with Ag processing (TAP) translocates proteasomally derived cytosolic peptides into the endoplasmic reticulum. TAP is a central component of the peptide-loading complex (PLC), to which tapasin (TPN) recruits MHC class I (MHC I) and accessory chaperones. The PLC functions to facilitate and optimize MHC I-mediated Ag presentation. The heterodimeric peptide transporter consists of two homologous subunits, TAP1 and TAP2, each of which contains an N-terminal domain (N-domain) in addition to a conserved transmembrane (TM) core segment. Each N-domain binds to the TM region of a single TPN molecule, which recruits one MHC I molecule to TAP1 and/or TAP2. Although both N-domains act as TPN-docking sites, various studies suggest a functional asymmetry within the PLC resulting in greater significance of the TAP2/TPN interaction for MHC loading. In this study, we demonstrate that the leucine-rich hydrophobic sequence stretches (with the central leucine residues L20 and L66) in the first and second TM helix of TAP2 form a functional unit acting as a docking site for optimal TPN/MHC I recruitment, whereas three distinct highly conserved arginine and/or aspartate residues inside or flanking these TM helices are dispensable. Moreover, we show that the physical interaction between TAP2 and TPN is disrupted by benzene, a compound known to interfere with hydrophobic interactions, such as those between pairing leucine zippers. No such effects were observed for the TAP1/TAP2 interaction or the complex formation between TPN and MHC I. We propose that TAP/TPN complex formation is driven by hydrophobic interactions via leucine zipper-like motifs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 3
  • ATP-Binding Cassette Transporters / metabolism*
  • ATP-Binding Cassette Transporters / ultrastructure
  • Benzene / chemistry
  • Binding Sites / immunology
  • Biological Transport / immunology
  • Cell Line
  • Endoplasmic Reticulum / immunology
  • Histocompatibility Antigens Class I / immunology
  • Humans
  • Hydrophobic and Hydrophilic Interactions
  • Leucine Zippers / drug effects
  • Leucine Zippers / genetics
  • Membrane Transport Proteins / metabolism*
  • Membrane Transport Proteins / ultrastructure
  • Multiprotein Complexes / drug effects
  • Multiprotein Complexes / metabolism
  • Multiprotein Complexes / ultrastructure*
  • Protein Binding / immunology
  • Protein Structure, Tertiary

Substances

  • ATP Binding Cassette Transporter, Subfamily B, Member 3
  • ATP-Binding Cassette Transporters
  • Histocompatibility Antigens Class I
  • Membrane Transport Proteins
  • Multiprotein Complexes
  • tapasin
  • TAP2 protein, human
  • Benzene