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J Biol Chem ; 280(6): 4188-94, 2005 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-15556932

RESUMO

Class II major histocompatibility complex proteins bind peptides for presentation to T-cells as part of the immune response process. Monoclonal antibody MEM-265 recognizes the peptide-free conformation of the major histocompatibility complex class II protein HLA-DR1 through specific binding to an epitope contained between residues 50-67 of the beta-chain. In previous work using alanine scanning (1), we identified residues Leu-53, Asp-57, Tyr-60, Trp-61, Ser-63, and Leu-67 as essential for specific recognition by MEM-265. The spacing of these residues approximates a 3.5-residue repeat, suggesting that MEM-265 may recognize the epitope in an alpha-helical conformation. In the folded, peptide-loaded DR1 structure, the beta-chain residues 50-67 contain a kinked alpha-helical segment spanning Glu-52-Ser-63 (2). However, the conformation of this segment in the peptide-free form is unknown. We have used a new surface plasmon resonance approach in a SpotMatrix format to compare the kinetic rates and affinities for 18 alanine scanning mutants comprising epitope residues 50-67. In addition to the six essential residues described previously, we found two additional residues, Glu-52 and Gln-64, that contribute by enhancing MEM-265 binding. By contrast, mutation of either Gly-54 or Pro-56 to an alanine actually improved binding to MEM-265. In essentially all cases peptide substitutions that either improve or reduce MEM-265 recognition could be traced to differences in the dissociation rate (k off). The kinetic details of the present study support the presence of a structural component in the antigenic epitope recognized by MEM-265 in the peptide-free form of major histocompatibility complex II DR1 beta-chain.


Assuntos
Anticorpos Monoclonais/química , Epitopos/química , Ressonância de Plasmônio de Superfície/instrumentação , Ressonância de Plasmônio de Superfície/métodos , Alanina/química , Animais , Técnicas Biossensoriais , Biotinilação , Mapeamento de Epitopos/métodos , Glicina/química , Hibridomas/imunologia , Cinética , Ligantes , Camundongos , Modelos Químicos , Modelos Moleculares , Mutação , Peptídeos/química , Prolina/química , Ligação Proteica , Conformação Proteica , Estrutura Secundária de Proteína , Fatores de Tempo
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