Stoichiometric tapasin interactions in the catalysis of major histocompatibility complex class I molecule assembly.
The assembly of major histocompatibility complex (MHC) class I molecules with their peptide ligands in the endoplasmic reticulum (ER) requires the assistance of many proteins that form a multimolecular assemblage termed the 'peptide-loading complex'. Tapasin is the central stabilizer of this complex, which also includes the transporter associated with antigen processing (TAP), MHC class I molecules, the ER chaperone, calreticulin, and the thiol-oxidoreductase ERp57. In the present report, we investigated the requirements of these interactions for tapasin protein stability and MHC class I dissociation from the peptide-loading complex. We established that tapasin is stable in the absence of either TAP or MHC class I interaction. In the absence of TAP, tapasin interaction with MHC class I molecules is long-lived and results in the sequestration of existing tapasin molecules. In contrast, in TAP-sufficient cells, tapasin is re-utilized to interact with and facilitate the assembly of many MHC class I molecules sequentially. Furthermore, chemical cross-linking has been utilized to characterize the interactions within this complex. We demonstrate that tapasin and MHC class I molecules exist in a 1 : 1 complex without evidence of higher-order tapasin multimers. Together these studies shed light on the tapasin protein life cycle and how it functions in MHC class I assembly with peptide for presentation to CD8(+) T cells.
Bangia
Naveen
N
Department of Immunology, Roswell Park Cancer Institute, Buffalo, NY 14263, USA. naveen.bangia@roswellpark.org
Cresswell
Peter
P
D018528:ATP-Binding Cassette Transporters; D017951:Antigen Presentation; D017920:Antiporters / Q000276:immunology / Q000378:metabolism*; D002384:Catalysis; D015395:Histocompatibility Antigens Class I / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D007136:Immunoglobulins / Q000276:immunology / Q000378:metabolism*; D026901:Membrane Transport Proteins; D011485:Protein Binding / Q000276:immunology; D014407:Tumor Cells, Cultured
D018528:ATP-Binding Cassette Transporters; D017920:Antiporters; D015395:Histocompatibility Antigens Class I; D007136:Immunoglobulins; D026901:Membrane Transport Proteins; C107762:tapasin; C477327:transporter associated with antigen processing (TAP)
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