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

Elke Rufer, Danny Kägebein, Ralf M Leonhardt, Michael R Knittler

Journal of immunology (Baltimore, Md. : 1950) 2015 Dec 1

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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. Copyright © 2015 by The American Association of Immunologists, Inc.

Citation

Elke Rufer, Danny Kägebein, Ralf M Leonhardt, Michael R Knittler. Hydrophobic Interactions Are Key To Drive the Association of Tapasin with Peptide Transporter Subunit TAP2. Journal of immunology (Baltimore, Md. : 1950). 2015 Dec 1;195(11):5482-94