Qualitative and quantitative differences in peptides bound to HLA-B27 in the presence of mouse versus human tapasin define a role for tapasin as a size-dependent peptide editor.
Tapasin (Tpn) is a chaperone of the endoplasmic reticulum involved in peptide loading to MHC class I proteins. The influence of mouse Tpn (mTpn) on the HLA-B*2705-bound peptide repertoire was analyzed to characterize the species specificity of this chaperone. B*2705 was expressed on Tpn-deficient human 721.220 cells cotransfected with human (hTpn) or mTpn. The heterodimer to beta(2)-microglobulin-free H chain ratio on the cell surface was reduced with mTpn, suggesting lower B*2705 stability. The B*2705-bound peptide repertoires loaded with hTpn or mTpn shared 94-97% identity, although significant differences in peptide amount were observed in 16-17% of the shared ligands. About 3-6% of peptides were bound only with either hTpn or mTpn. Nonamers differentially bound with mTpn had less suitable anchor residues and bound B*2705 less efficiently in vitro than those loaded only with hTpn or shared nonamers. Decamers showed a different pattern: those found only with mTpn had similarly suitable residues as shared decamers and bound B*2705 with high efficiency. Peptides differentially presented by B*2705 on human or mouse cells showed an analogous pattern of residue suitability, suggesting that the effect of mTpn on B*2705 loading is comparable in both cell types. Thus, mTpn has quantitative and qualitative effects on the B*2705-bound peptide repertoire, impairing presentation of some suitable ligands and allowing others with suboptimal anchor residues and lower affinity to be presented. Our results favor a size-dependent peptide editing role of Tpn for HLA-B*2705 that is species-dependent and suboptimally performed, at least for nonamers, by mTpn.
Sesma
Laura
L
Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid), Facultad de Ciencias, Universidad Autónoma, Madrid, Spain.
Galocha
Begoña
B
Vázquez
Miriam
M
Purcell
Anthony W
AW
Marcilla
Miguel
M
McCluskey
James
J
López de Castro
José A
JA
D000818:Animals; D017951:Antigen Presentation / Q000235:genetics; D017920:Antiporters / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D015235:HLA-B Antigens / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015796:HLA-B27 Antigen; D006801:Humans; D007136:Immunoglobulins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D008024:Ligands; D026901:Membrane Transport Proteins; D051379:Mice; D018832:Molecular Chaperones / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D009842:Oligopeptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D017393:RNA Editing / Q000276:immunology; D013045:Species Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014162:Transfection
D017920:Antiporters; D015235:HLA-B Antigens; C464936:HLA-B*27:05 antigen; D015796:HLA-B27 Antigen; D007136:Immunoglobulins; D008024:Ligands; D026901:Membrane Transport Proteins; D018832:Molecular Chaperones; D009842:Oligopeptides; C107762:tapasin