title: Structural and functional consequences of altering a peptide MHC anchor residue.
abstract: To better understand TCR discrimination of multiple ligands, we have analyzed the crystal structures of two Hb peptide/I-E(k) complexes that differ by only a single amino acid substitution at the P6 anchor position within the peptide (E73D). Detailed comparison of multiple independently determined structures at 1.9 A resolution reveals that removal of a single buried methylene group can alter a critical portion of the TCR recognition surface. Significant variance was observed in the peptide P5-P8 main chain as well as a rotamer difference at LeuP8, approximately 10 A distal from the substitution. No significant variations were observed in the conformation of the two MHC class II molecules. The ligand alteration results in two peptide/MHC complexes that generate bulk T cell responses that are distinct and essentially nonoverlapping. For the Hb-specific T cell 3.L2, substitution reduces the potency of the ligand 1000-fold. Soluble 3.L2 TCR binds the two peptide/MHC complexes with similar affinity, although with faster kinetics. These results highlight the role of subtle variations in MHC Ag presentation on T cell activation and signaling.
authors.affiliation: Department of Pathology and Center for Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Kersh
authors.forename: M J
authors.initials: MJ
authors.lastname: Miley
authors.forename: C A
authors.initials: CA
authors.lastname: Nelson
authors.forename: A
authors.initials: A
authors.lastname: Grakoui
authors.forename: S
authors.initials: S
authors.lastname: Horvath
authors.forename: D L
authors.initials: DL
authors.lastname: Donermeyer
authors.forename: J
authors.initials: J
authors.lastname: Kappler
authors.forename: P M
authors.initials: PM
authors.lastname: Allen
authors.forename: D H
authors.initials: DH
authors.lastname: Fremont
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000276:immunology*; D000818:Animals; D017951:Antigen Presentation; D001224:Aspartic Acid / Q000378:metabolism; D002478:Cells, Cultured; D018360:Crystallography, X-Ray; D018698:Glutamic Acid / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D051379:Mice; D008808:Mice, Inbred CBA; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology* / Q000378:metabolism*; D011487:Protein Conformation; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D000949:Histocompatibility Antigens Class II; C024138:I-E-antigen; D008024:Ligands; D010455:Peptides; D011948:Receptors, Antigen, T-Cell; D001224:Aspartic Acid; D018698:Glutamic Acid