title: A charged amino acid residue in the transmembrane/cytoplasmic region of tapasin influences MHC class I assembly and maturation.
abstract: Tapasin influences the quantity and quality of MHC/peptide complexes at the cell surface; however, little is understood about the structural features that underlie its effects. Because tapasin, MHC class I, and TAP are transmembrane proteins, the tapasin transmembrane/cytoplasmic region has the potential to affect interactions at the endoplasmic reticulum membrane. In this study, we have assessed the influence of a conserved lysine at position 408, which lies in the tapasin transmembrane/cytoplasmic domain. We found that substitutions at position K408 in tapasin affected the expression of MHC class I molecules at the cell surface, and down-regulated tapasin stabilization of TAP. In addition to affecting TAP interaction with tapasin, the substitution of alanine, but not tryptophan, for the lysine at tapasin position 408 increased the amount of tapasin found in association with the open, peptide-free form of the HLA-B8 H chain. Tapasin K408A was also associated with more folded, beta(2)-microglobulin-assembled HLA-B8 molecules than wild-type tapasin. Consistent with our observation of a large pool of tapasin K408A-associated HLA-B8 molecules, the rate at which HLA-B8 migrated from the endoplasmic reticulum was slower in tapasin K408A-expressing cells than in wild-type tapasin-expressing cells. Thus, the alanine substitution at position 408 in tapasin may interfere with the stable acquisition by MHC class I molecules of peptides that are sufficiently optimal to allow MHC class I release from tapasin.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha 68198, USA.
authors.forename: Jason L
authors.initials: JL
authors.lastname: Petersen
authors.forename: Heather D
authors.initials: HD
authors.lastname: Hickman-Miller
authors.forename: Mary M
authors.initials: MM
authors.lastname: McIlhaney
authors.forename: Shanna E
authors.initials: SE
authors.lastname: Vargas
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Purcell
authors.forename: William H
authors.initials: WH
authors.lastname: Hildebrand
authors.forename: Joyce C
authors.initials: JC
authors.lastname: Solheim
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D017920:Antiporters / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry* / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006680:HLA Antigens / Q000737:chemistry / Q000378:metabolism*; D015795:HLA-B8 Antigen / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007136:Immunoglobulins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007535:Isomerases / Q000378:metabolism; D008239:Lysine / Q000737:chemistry* / Q000235:genetics; D026901:Membrane Transport Proteins; D051379:Mice; D008969:Molecular Sequence Data; D019704:Protein Disulfide-Isomerases; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D014364:Tryptophan / Q000235:genetics; D015854:Up-Regulation / Q000235:genetics
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D017920:Antiporters; D006680:HLA Antigens; D015795:HLA-B8 Antigen; D006360:Heat-Shock Proteins; D015395:Histocompatibility Antigens Class I; D007136:Immunoglobulins; D026901:Membrane Transport Proteins; C073119:TAP1 protein, human; C107762:tapasin; C071692:TAP2 protein, human; D014364:Tryptophan; D007535:Isomerases; C513195:Pdia3 protein, mouse; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human; D008239:Lysine; D000409:Alanine