title: Mutations changing the kinetics of class II MHC peptide exchange.
abstract: IE/DR MHC class II molecules have an extensive H-bonding network under the bound peptide. In IE(k), two alpha chain acidic amino acids in the core of this network were mutated to amides. At low pH, the mutant molecule exchanged peptide much more rapidly than the wild-type. The crystal structure of the mutant IE(k) revealed the loss of a single buried water molecule and a reorganization of the predicted H-bonding network. We suggest that these mutations enhance the transition of MHC class II to an open conformation at low pH allowing the bound peptide to escape. In wild-type IE(k), the need to protonate these amino acids also may be a bottleneck in the return to a closed conformation after peptide binding.
authors.affiliation: Howard Hughes Medical Institute, Integrated Department of Immunology, Zuckerman Family/Canyon, Ranch Crystallography Laboratory, National Jewish Medical and Research Center, Denver, CO 80206, USA.
authors.forename: N
authors.initials: N
authors.lastname: Wilson
authors.forename: D
authors.initials: D
authors.lastname: Fremont
authors.forename: P
authors.initials: P
authors.lastname: Marrack
authors.forename: J
authors.initials: J
authors.lastname: Kappler
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010455:Peptides / Q000276:immunology*; D017433:Protein Structure, Secondary
chemical_list: D000949:Histocompatibility Antigens Class II; C024138:I-E-antigen; D010455:Peptides