title: Chemical identification of a low abundance lysozyme peptide family bound to I-Ak histocompatibility molecules.
abstract: The processing by antigen-presenting cells (APC) of the protein hen egg-white lysozyme (HEL) results in the selection of a number of peptide families by the class II major histocompatibility complex (MHC) molecule, I-A(k). Some of these families are expressed in very small amounts, in the order of a few picomoles/10(9) APC. We detected these peptides from an extract of class II MHC molecules by using monoclonal anti-peptide antibodies to capture the MHC-bound peptides prior to their examination by HPLC tandem mass spectrometry. Here, we have identified several members of a family of peptides encompassing residues 20-35, which represent less than 1% of the total HEL peptides. Binding analysis indicated that the core segment of the family was represented by residues 24-32 (SLGNWVCAA). Asn-27 (shown in boldface) is the main MHC-binding residue, mapped as interacting with the P4 pocket of the I-A(k) molecule. Analysis of several T cell hybridomas indicated that three residues contacted the T cell receptor: Tyr-23 (P-1), Leu-25 (P3), and Trp-28 (P5). The HEL peptides isolated from the APC extract were sulfated on Tyr-23, but further analysis showed that this modification did not occur physiologically but took place during the peptide isolation.
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, Washington University, St. Louis, Missouri 63110, USA.
authors.forename: Carlos
authors.initials: C
authors.lastname: Velazquez
authors.forename: Ilan
authors.initials: I
authors.lastname: Vidavsky
authors.forename: Koen
authors.initials: K
authors.lastname: van der Drift
authors.forename: Michael L
authors.initials: ML
authors.lastname: Gross
authors.forename: Emil R
authors.initials: ER
authors.lastname: Unanue
mesh_terms: D000409:Alanine; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002645:Chickens; D000939:Epitopes / Q000737:chemistry / Q000378:metabolism; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D016393:Lymphoma, B-Cell; D051379:Mice; D009113:Muramidase / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry; D010766:Phosphorylation; D013431:Sulfates / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D010446:Peptide Fragments; D013431:Sulfates; D009113:Muramidase; D000409:Alanine