title: Monoclonal antibodies specific for the empty conformation of HLA-DR1 reveal aspects of the conformational change associated with peptide binding.
abstract: Class II major histocompatibility complex (MHC) proteins bind peptides and present them at the cell surface for interaction with CD4+ T cells as part of the system by which the immune system surveys the body for signs of infection. Peptide binding is known to induce conformational changes in class II MHC proteins on the basis of a variety of hydrodynamic and spectroscopic approaches, but the changes have not been clearly localized within the overall class II MHC structure. To map the peptide-induced conformational change for HLA-DR1, a common human class II MHC variant, we generated a series of monoclonal antibodies recognizing the beta subunit that are specific for the empty conformation. Each antibody reacted with the empty but not the peptide-loaded form, for both soluble recombinant protein and native protein expressed at the cell surface. Antibody binding epitopes were characterized using overlapping peptides and alanine scanning substitutions and were localized to two distinct regions of the protein. The pattern of key residues within the epitopes suggested that the two epitope regions undergo substantial conformational alteration during peptide binding. These results illuminate aspects of the structure of the empty forms and the nature of the peptide-induced conformational change.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Carven
authors.forename: Sriram
authors.initials: S
authors.lastname: Chitta
authors.forename: Ivan
authors.initials: I
authors.lastname: Hilgert
authors.forename: Mia M
authors.initials: MM
authors.lastname: Rushe
authors.forename: Rick F
authors.initials: RF
authors.lastname: Baggio
authors.forename: Michelle
authors.initials: M
authors.lastname: Palmer
authors.forename: Jaime E
authors.initials: JE
authors.lastname: Arenas
authors.forename: Jack L
authors.initials: JL
authors.lastname: Strominger
authors.forename: Vaclav
authors.initials: V
authors.lastname: Horejsi
authors.forename: Laura
authors.initials: L
authors.lastname: Santambrogio
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Stern
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000918:Antibody Specificity; D018604:Epitope Mapping; D000939:Epitopes; D015798:HLA-DR1 Antigen / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000276:immunology; D011485:Protein Binding / Q000276:immunology; D011487:Protein Conformation
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D015798:HLA-DR1 Antigen; D010455:Peptides