title: Identification of peptide superagonists for a self-K-ras-reactive CD4+ T cell clone using combinatorial peptide libraries and mass spectrometry.
abstract: The proliferative responses of a human CD4+ T cell clone 29.15.2, reactive with a self-K-ras-derived peptide (3EYKLVVVGAGGVGKSALT20), were tested using a set of X9 combinatorial peptide libraries containing the flanking residues (EYKLVXXXXXXXXXSALT, where X indicates random amino acids). Certain peptide libraries, such as EYKLVXXXXXX<cmd UNL>M<cmd /UNL> XXSALT and EYKLVXXXXXXX<cmd UNL>H<cmd /UNL> XSALT, stimulated a marked proliferation of 29.15.2. However, no combinations of substitutions tested, such as EYKLVXXXXXX<cmd UNL>MH<cmd /UNL> XSALT, exhibited additive effects. We subsequently synthesized peptides with degenerate sequences (a mixture of 480 species), where each position is composed of the wild-type (wt) residue or of amino acids that induced the proliferation of 29.15.2, in positional scanning. Interestingly, one fraction of degenerate peptides, separated by reverse-phase HPLC, stimulated much higher proliferation than did the wt; in addition, the retention time of this fraction was distinct from that of the wt. Mass spectrometry analysis of this fraction and flanking fractions identified five peptide species that exhibit strong signals in a manner that parallels the antigenic activity. Finally, 17 candidate peptide sequences were deduced from mass spectrometry and hydrophobicity scoring results, of which two peptides (EYKLVVVGAGG<cmd UNL>ML<cmd /UNL> KSALT and EYKLVVVGAGG<cmd UNL>MI<cmd /UNL> KSALT) did induce 52- and 61-fold stronger proliferation, respectively, compared with the wt. These findings indicate that: 1) synthetic peptides that carry "the best" residue substitution at each position of combinatorial peptide libraries do not always exhibit superagonism, and 2) such a drawback can be overcome with the use of mass spectrometry. This approach provides new perspectives for the accurate and efficient identification of peptide superagonists.
authors.affiliation: Division of Immunogenetics, Department of Neuroscience and Immunology, Kumamoto University Graduate School of Medical Sciences, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Tanaka
authors.forename: H
authors.initials: H
authors.lastname: Ohyama
authors.forename: M
authors.initials: M
authors.lastname: Ogawa
authors.forename: Y
authors.initials: Y
authors.lastname: Nishimura
authors.forename: S
authors.initials: S
authors.lastname: Matsushita
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002999:Clone Cells; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology; D013058:Mass Spectrometry / Q000379:methods; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000819:agonists / Q000138:chemical synthesis / Q000276:immunology / Q000378:metabolism; D019151:Peptide Library; D010455:Peptides / Q000819:agonists* / Q000138:chemical synthesis / Q000276:immunology* / Q000302:isolation & purification; D018631:ras Proteins / Q000819:agonists* / Q000138:chemical synthesis / Q000276:immunology* / Q000302:isolation & purification
chemical_list: D010446:Peptide Fragments; D019151:Peptide Library; D010455:Peptides; D018631:ras Proteins