title: pH-susceptibility of HLA-DO tunes DO/DM ratios to regulate HLA-DM catalytic activity.
abstract: The peptide-exchange catalyst, HLA-DM, and its inhibitor, HLA-DO control endosomal generation of peptide/class II major histocompatibility protein (MHC-II) complexes; these complexes traffic to the cell surface for inspection by CD4+ T cells. Some evidence suggests that pH influences DO regulation of DM function, but pH also affects the stability of polymorphic MHC-II proteins, spontaneous peptide loading, DM/MHC-II interactions and DM catalytic activity, imposing challenges on approaches to determine pH effects on DM-DO function and their mechanistic basis. Using optimized biochemical methods, we dissected pH-dependence of spontaneous and DM-DO-mediated class II peptide exchange and identified an MHC-II allele-independent relationship between pH, DO/DM ratio and efficient peptide exchange. We demonstrate that active, free DM is generated from DM-DO complexes at late endosomal/lysosomal pH due to irreversible, acid-promoted DO destruction rather than DO/DM molecular dissociation. Any soluble DM that remains in complex with DO stays inert. pH-exposure of DM-DO in cell lysates corroborates such a pH-regulated mechanism, suggesting acid-activated generation of functional DM in DO-expressing cells.
authors.affiliation: Department of Pediatrics, Stanford University, Stanford, CA 94305, USA.|Stanford Program in Immunology, Stanford University, Stanford, CA 94305, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Jiang
authors.affiliation: Department of Pediatrics, Stanford University, Stanford, CA 94305, USA.|Stanford Program in Immunology, Stanford University, Stanford, CA 94305, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Strohman
authors.affiliation: Department of Pediatrics, Stanford University, Stanford, CA 94305, USA.
authors.forename: Sriram
authors.initials: S
authors.lastname: Somasundaram
authors.affiliation: Department of Pediatrics, Stanford University, Stanford, CA 94305, USA.
authors.forename: Sashi
authors.initials: S
authors.lastname: Ayyangar
authors.affiliation: Department of Pediatrics, Stanford University, Stanford, CA 94305, USA.
authors.forename: Tieying
authors.initials: T
authors.lastname: Hou
authors.affiliation: Department of Pediatrics, Stanford University, Stanford, CA 94305, USA.
authors.forename: Nan
authors.initials: N
authors.lastname: Wang
authors.affiliation: Department of Pediatrics, Stanford University, Stanford, CA 94305, USA.|Stanford Program in Immunology, Stanford University, Stanford, CA 94305, USA.
authors.forename: Elizabeth D
authors.initials: ED
authors.lastname: Mellins
mesh_terms: D000595:Amino Acid Sequence; D017951:Antigen Presentation; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology; D020134:Catalytic Domain; D003713:Dendritic Cells / Q000166:cytology / Q000276:immunology; D015870:Gene Expression / Q000276:immunology; D006681:HLA-D Antigens / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007118:Immunoassay; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology
chemical_list: D006681:HLA-D Antigens; C084245:HLA-DM antigens; C046148:HLA-DO antigens; D010455:Peptides; D011994:Recombinant Proteins