title: Influence of the tapasin C terminus on the assembly of MHC class I allotypes.
abstract: Several endoplasmic reticulum proteins, including tapasin, play an important role in major histocompatibility complex (MHC) class I assembly. In this study, we assessed the influence of the tapasin cytoplasmic tail on three mouse MHC class I allotypes (H2-K(b), -K(d), and -L(d)) and demonstrated that the expression of truncated mouse tapasin in mouse cells resulted in very low K(b), K(d), and L(d) surface expression. The surface expression of K(d) also could not be rescued by human soluble tapasin, suggesting that the surface expression phenotype of the mouse MHC class I molecules in the presence of soluble tapasin was not due to mouse/human differences in tapasin. Notably, soluble mouse tapasin was able to partially rescue HLA-B8 surface expression on human 721.220 cells. Thus, the cytoplasmic tail of tapasin (either mouse or human) has a stronger impact on the surface expression of murine MHC class I molecules on mouse cells than on the expression of HLA-B8 on human cells. A K408W mutation in the mouse tapasin transmembrane/cytoplasmic domain disrupted K(d) folding and release from tapasin, but not interaction with transporter associated with antigen processing (TAP), indicating that the mechanism whereby the tapasin transmembrane/cytoplasmic domain facilitates MHC class I assembly is not limited to TAP stabilization. Our findings indicate that the C terminus of mouse tapasin plays a vital role in enabling murine MHC class I molecules to be expressed at the surface of mouse cells.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases and Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, 986805 Nebraska Medical Center, Omaha, NE 68198-6805, USA.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Simone
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Wang
authors.forename: Amit
authors.initials: A
authors.lastname: Tuli
authors.forename: Mary M
authors.initials: MM
authors.lastname: McIlhaney
authors.forename: Joyce C
authors.initials: JC
authors.lastname: Solheim
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000502:physiology; D019943:Amino Acid Substitution; D000818:Animals; D017951:Antigen Presentation; D000954:Antigens, Surface / Q000378:metabolism; D002460:Cell Line; D006183:H-2 Antigens / Q000378:metabolism*; D015795:HLA-B8 Antigen / Q000378:metabolism; D064532:Histocompatibility Antigen H-2D; D006801:Humans; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D020125:Mutation, Missense; D017354:Point Mutation; D017510:Protein Folding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012995:Solubility; D013045:Species Specificity
chemical_list: D018528:ATP-Binding Cassette Transporters; D000954:Antigens, Surface; D006183:H-2 Antigens; C024755:H-2K(K) antigen; C032876:H-2Kb protein, mouse; D015795:HLA-B8 Antigen; D064532:Histocompatibility Antigen H-2D; D026901:Membrane Transport Proteins; D011993:Recombinant Fusion Proteins; C107762:tapasin; C477327:transporter associated with antigen processing (TAP)