Structural arrangement of the transmission interface in the antigen ABC transport complex TAP.
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.
Oancea
Giani
G
Institute of Biochemistry, Biocenter, Johann Wolfgang Goethe-Universität, Max-von-Laue-Strasse 9, D-60438 Frankfurt/Main, Germany.
O'Mara
Megan L
ML
Bennett
W F Drew
WF
Tieleman
D Peter
DP
Abele
Rupert
R
Tampé
Robert
R
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*
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