title: Structural arrangement of the transmission interface in the antigen ABC transport complex TAP.
abstract: The transporter associated with antigen processing (TAP) represents a focal point in the immune recognition of virally or malignantly transformed cells by translocating proteasomal degradation products into the endoplasmic reticulum-lumen for loading of MHC class I molecules. Based on a number of experimental data and the homology to the bacterial ABC exporter Sav1866, we constructed a 3D structural model of the core TAP complex and used it to examine the interface between the transmembrane and nucleotide-binding domains (NBD) by cysteine-scanning and cross-linking approaches. Herein, we demonstrate the functional importance of the newly identified X-loop in the NBD in coupling substrate binding to downstream events in the transport cycle. We further verified domain swapping in a heterodimeric ABC half-transporter complex by cysteine cross-linking. Strikingly, either substrate binding or translocation can be blocked by cross-linking the X-loop to coupling helix 2 or 1, respectively. These results resolve the structural arrangement of the transmission interface and point to different functions of the cytosolic loops and coupling helices in substrate binding, signaling, and transport.
authors.affiliation: Institute of Biochemistry, Biocenter, Johann Wolfgang Goethe-Universität, Max-von-Laue-Strasse 9, D-60438 Frankfurt/Main, Germany.
authors.forename: Giani
authors.initials: G
authors.lastname: Oancea
authors.forename: Megan L
authors.initials: ML
authors.lastname: O'Mara
authors.forename: W F Drew
authors.initials: WF
authors.lastname: Bennett
authors.forename: D Peter
authors.initials: DP
authors.lastname: Tieleman
authors.forename: Rupert
authors.initials: R
authors.lastname: Abele
authors.forename: Robert
authors.initials: R
authors.lastname: Tampé
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism; D003432:Cross-Linking Reagents; D006801:Humans; D008958:Models, Molecular; D016296:Mutagenesis; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013211:Staphylococcus aureus / Q000737:chemistry*
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D003432:Cross-Linking Reagents; C073119:TAP1 protein, human; C477327:transporter associated with antigen processing (TAP); C071692:TAP2 protein, human