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Chemical Identification of a Low Abundance Lysozyme Peptide Family Bound to I-Ak Histocompatibility Molecules

2002; Elsevier BV; Volume: 277; Issue: 45 Linguagem: Inglês

10.1074/jbc.m202316200

1083-351X

Carlos Velázquez, Ilan Vidavsky, Koen van der Drift, Michael L. Gross, Emil R. Unanue,

vaccines and immunoinformatics approaches

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-Ak. Some of these families are expressed in very small amounts, in the order of a few picomoles/109 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-Ak 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.