title: Hydrophobic Interactions Are Key To Drive the Association of Tapasin with Peptide Transporter Subunit TAP2.
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.
authors.affiliation: Institute of Immunology, Federal Research Institute of Animal Health, Friedrich Loeffler Institute, D-17493 Greifswald-Isle of Riems, Germany;
authors.forename: Elke
authors.initials: E
authors.lastname: Rufer
authors.affiliation: Institute of Immunology, Federal Research Institute of Animal Health, Friedrich Loeffler Institute, D-17493 Greifswald-Isle of Riems, Germany;
authors.forename: Danny
authors.initials: D
authors.lastname: Kägebein
authors.affiliation: Howard Hughes Medical Institute, New Haven, CT 06519; and Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06519.
authors.forename: Ralf M
authors.initials: RM
authors.lastname: Leonhardt
authors.affiliation: Institute of Immunology, Federal Research Institute of Animal Health, Friedrich Loeffler Institute, D-17493 Greifswald-Isle of Riems, Germany; michael.knittler@fli.bund.de.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Knittler
mesh_terms: D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism* / Q000648:ultrastructure; D001554:Benzene / Q000737:chemistry; D001665:Binding Sites / Q000276:immunology; D001692:Biological Transport / Q000276:immunology; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000276:immunology; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D016350:Leucine Zippers / Q000187:drug effects / Q000235:genetics; D026901:Membrane Transport Proteins / Q000378:metabolism* / Q000648:ultrastructure; D046912:Multiprotein Complexes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D011485:Protein Binding / Q000276:immunology; D017434:Protein Structure, Tertiary
chemical_list: D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D015395:Histocompatibility Antigens Class I; D026901:Membrane Transport Proteins; D046912:Multiprotein Complexes; C107762:tapasin; C071692:TAP2 protein, human; D001554:Benzene