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Structural arrangement of the transmission interface in the antigen ABC transport complex TAP

By Giani Oancea, Megan L. O'Mara, W. F. Drew Bennett, D. Peter Tieleman, Rupert Abele and Robert Tampé

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

Topics: Biological Sciences
Publisher: National Academy of Sciences
OAI identifier: oai:pubmedcentral.nih.gov:2657591
Provided by: PubMed Central
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