TAP association influences the conformation of nascent MHC class I molecules.
The influence of TAP-MHC class I interactions on peptide binding to the class I heavy chain is assessed during TAP-dependent assembly using Kb-specific Abs that recognize conformational changes induced by assembly with beta2-microglobulin (beta2m) and by peptide binding. A significant portion (45%) of Kb molecules in TAP+, RMA-derived microsomes are associated with the TAP complex as measured by coimmunoisolation of Kb using anti-TAP1 Abs, while only 20% of the Kb heavy chain molecules are isolated as Kbbeta2m complexes with the alpha-Kb-specific Abs, Y-3 or K-10-56. The amount of Kb isolated with Y-3 and K-10-56 increases in proportion to transport and binding of peptide to the Kb molecules within the RMA microsomes. In contrast, less than 5% of the Kb within TAP2-RMA-S microsomes associated with the remaining TAP1 subunit. However, greater than 60% of Kb heavy chain is isolated as K-10-56- and Y-3-reactive Kbbeta2m complexes. We propose that a TAP-MHC class I interaction serves to stabilize the MHC class I:beta2m complex in an immature conformation (Y-3 and K-10-56 nonreactive) prior to high affinity peptide binding, preventing the export of class I molecules complexed with low affinity peptide ligands from the ER.
Owen
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BA
Department of Biochemistry and Molecular Biology, Mayo Clinic/Foundation, Rochester, MN 55905, USA.
Pease
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LR
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D000236:Adenoma; D000818:Animals; D006183:H-2 Antigens / Q000737:chemistry / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000737:chemistry* / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D008861:Microsomes / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000276:immunology; D011487:Protein Conformation; D014407:Tumor Cells, Cultured; D001613:beta 2-Microglobulin / Q000737:chemistry / Q000378:metabolism
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D006183:H-2 Antigens; C032876:H-2Kb protein, mouse; D015395:Histocompatibility Antigens Class I; D008024:Ligands; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse; D001613:beta 2-Microglobulin