title: Assembly of tapasin-associated MHC class I in the absence of the transporter associated with antigen processing (TAP).
abstract: The assembly of MHC class I molecules is regulated by a multi-protein complex in the endoplasmic reticules (ER) termed the loading complex. Tapasin is suggested to be one of the molecules forming this complex on the basis of its interaction with both the transporter associated with antigen processing (TAP) and MHC class I molecules. To address whether TAP is indispensable for the processing of the assembly of tapasin-associated MHC class I molecules, we studied the association of MHC class I molecules with tapasin, the assembly of tapasin-associated MHC class I with peptides and the peptide-mediated dissociation of MHC class I from tapasin in TAP-mutant T2 cells. In the absence of TAP, MHC class I heavy chain and beta(2)-microglobulin dimers were found to be properly associated with tapasin. The stable MHC class I dimer was required for its association with tapasin in the ER. In the absence of TAP, tapasin retained MHC class I molecules much longer in the ER than in the presence of TAP. This low off-rate of MHC class I from tapasin was due to the absence of high-affinity peptides in the ER of TAP-mutant cells but not to the absence of TAP per se. The introduction of peptides into permeabilized microsomes of TAP-mutant cells led to effective loading of the peptides onto tapasin-associated MHC class I and to the subsequent dissociation of MHC class I from tapasin. These results demonstrate that regulation of the assembly of tapasin-associated MHC class I is independent of the interaction of tapasin with TAP, but is dependent upon the peptides transported by TAP.
authors.affiliation: Tumor Immunology, Lund University, Solvegatan 21, 223 62 Lund, Sweden.
authors.forename: K M
authors.initials: KM
authors.lastname: Paulsson
authors.forename: P O
authors.initials: PO
authors.lastname: Anderson
authors.forename: S
authors.initials: S
authors.lastname: Chen
authors.forename: H O
authors.initials: HO
authors.lastname: Sjögren
authors.forename: H G
authors.initials: HG
authors.lastname: Ljunggren
authors.forename: P
authors.initials: P
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Li
mesh_terms: D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D000255:Adenosine Triphosphate / Q000502:physiology; D017951:Antigen Presentation / Q000235:genetics; D017920:Antiporters / Q000378:metabolism*; D002460:Cell Line; D006680:HLA Antigens / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009154:Mutation; D010455:Peptides / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000276:immunology
chemical_list: D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D017920:Antiporters; D006680:HLA Antigens; D015395:Histocompatibility Antigens Class I; D007136:Immunoglobulins; D026901:Membrane Transport Proteins; D010455:Peptides; C107762:tapasin; C071692:TAP2 protein, human; D000255:Adenosine Triphosphate