title: Evaluating the Role of HLA-DM in MHC Class II-Peptide Association Reactions.
abstract: Ag presentation by MHC class II (MHC II) molecules to CD4(+) T cells plays a key role in the regulation of the adaptive immune response. Loading of antigenic peptides onto MHC II is catalyzed by HLA-DM (DM), a nonclassical MHC II molecule. The mechanism of DM-facilitated peptide loading is an outstanding problem in the field of Ag presentation. In this study, we systemically explored possible kinetic mechanisms for DM-catalyzed peptide association by measuring real-time peptide association kinetics using fluorescence polarization assays and comparing the experimental data with numerically modeled peptide association reactions. We found that DM does not facilitate peptide association by stabilizing peptide-free MHC II against aggregation. Moreover, DM does not promote transition of an inactive peptide-averse conformation of MHC II to an active peptide-receptive conformation. Instead, DM forms an intermediate with MHC II that binds peptide with faster kinetics than MHC II in the absence of DM. In the absence of peptides, interaction of MHC II with DM leads to inactivation and formation of a peptide-averse form. This study provides novel insights into how DM efficiently catalyzes peptide loading during Ag presentation.
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA 01605; and.
authors.forename: Liusong
authors.initials: L
authors.lastname: Yin
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA 01605; and.
authors.forename: Zachary J
authors.initials: ZJ
authors.lastname: Maben
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA 01605; and.
authors.forename: Aniuska
authors.initials: A
authors.lastname: Becerra
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA 01605; and Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605 lawrence.stern@umassmed.edu.
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Stern
mesh_terms: D000595:Amino Acid Sequence; D017951:Antigen Presentation; D001665:Binding Sites; D016231:Fluorescence Polarization Immunoassay; D005786:Gene Expression Regulation; D006681:HLA-D Antigens / Q000737:chemistry* / Q000235:genetics; D015798:HLA-DR1 Antigen / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000235:genetics; D011485:Protein Binding; D021381:Protein Transport; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D015398:Signal Transduction; D012996:Solutions
chemical_list: D006681:HLA-D Antigens; C084245:HLA-DM antigens; D015798:HLA-DR1 Antigen; D010455:Peptides; D011994:Recombinant Proteins; D012996:Solutions