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Catalysis of peptide dissociation from class II MHC-peptide complexes. 1999

L Schmitt, and J R Kratz, and M M Davis, and H M McConnell
Department of Chemistry, Stanford University, Stanford, CA 94305, USA.

Certain peptides such as dynorphin A [dynA-(1-13)] enhance the release of antigenic peptides bound to class II MHC molecules at neutral pH. This enhanced release has been termed push off. Previous work has shown that the antigenic pigeon cytochrome c peptide PCC-(89-104) has at least two conformational isomers when bound to the class II MHC protein I-Ek. We have accordingly studied the push off of PCC-(89-104) from the complex PCC-(89-104)/I-Ek to see whether these isomeric conformations are distinguished by the push-off effect. A comparison of the association and dissociation kinetics of PCC-(89-104)/I-Ek in the presence of dynA-(1-13) shows that dynA-(1-13) does not simply replace PCC-(89-104) but rather acts catalytically. The major product is peptide-free I-Ek, which is receptive to further peptide binding. Evidence is presented that a two peptide-one MHC complex is formed in solution. This ternary complex represents the first step of the mechanism of push off. 19F NMR data are presented that indicate that dynA-(1-13) interacts specifically with only one of the two isomeric complexes of PCC-(89-104) and I-Ek. A push-off mechanism is proposed in which dynA-(1-13) binds outside the peptide binding groove. In a second step, the dissociation of one of the two isomers is specifically enhanced. Thus the push-off effect may be useful for identifying conformational isomers and for separating them.

UI MeSH Term Description Entries
D007700 Kinetics The rate dynamics in chemical or physical systems.
D010446 Peptide Fragments Partial proteins formed by partial hydrolysis of complete proteins or generated through PROTEIN ENGINEERING techniques. Peptide Fragment,Fragment, Peptide,Fragments, Peptide
D010856 Columbidae Family in the order COLUMBIFORMES, comprised of pigeons or doves. They are BIRDS with short legs, stout bodies, small heads, and slender bills. Some sources call the smaller species doves and the larger pigeons, but the names are interchangeable. Columba livia,Doves,Pigeons,Domestic Pigeons,Feral Pigeons,Rock Doves,Rock Pigeons,Domestic Pigeon,Dove,Dove, Rock,Doves, Rock,Feral Pigeon,Pigeon,Pigeon, Domestic,Pigeon, Feral,Pigeon, Rock,Pigeons, Domestic,Pigeons, Feral,Pigeons, Rock,Rock Dove,Rock Pigeon
D011485 Protein Binding The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments. Plasma Protein Binding Capacity,Binding, Protein
D011487 Protein Conformation The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain). Conformation, Protein,Conformations, Protein,Protein Conformations
D003574 Cytochrome c Group A group of cytochromes with covalent thioether linkages between either or both of the vinyl side chains of protoheme and the protein. (Enzyme Nomenclature, 1992, p539) Cytochromes Type c,Group, Cytochrome c,Type c, Cytochromes
D006863 Hydrogen-Ion Concentration The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D000949 Histocompatibility Antigens Class II Large, transmembrane, non-covalently linked glycoproteins (alpha and beta). Both chains can be polymorphic although there is more structural variation in the beta chains. The class II antigens in humans are called HLA-D ANTIGENS and are coded by a gene on chromosome 6. In mice, two genes named IA and IE on chromosome 17 code for the H-2 antigens. The antigens are found on B-lymphocytes, macrophages, epidermal cells, and sperm and are thought to mediate the competence of and cellular cooperation in the immune response. The term IA antigens used to refer only to the proteins encoded by the IA genes in the mouse, but is now used as a generic term for any class II histocompatibility antigen. Antigens, Immune Response,Class II Antigens,Class II Histocompatibility Antigen,Class II Major Histocompatibility Antigen,Ia Antigens,Ia-Like Antigen,Ia-Like Antigens,Immune Response Antigens,Immune-Associated Antigens,Immune-Response-Associated Antigens,MHC Class II Molecule,MHC II Peptide,Class II Antigen,Class II Histocompatibility Antigens,Class II MHC Proteins,Class II Major Histocompatibility Antigens,Class II Major Histocompatibility Molecules,I-A Antigen,I-A-Antigen,IA Antigen,MHC Class II Molecules,MHC II Peptides,MHC-II Molecules,Antigen, Class II,Antigen, I-A,Antigen, IA,Antigen, Ia-Like,Antigens, Class II,Antigens, Ia,Antigens, Ia-Like,Antigens, Immune-Associated,Antigens, Immune-Response-Associated,I A Antigen,II Peptide, MHC,Ia Like Antigen,Ia Like Antigens,Immune Associated Antigens,Immune Response Associated Antigens,MHC II Molecules,Molecules, MHC-II,Peptide, MHC II,Peptides, MHC II
D017951 Antigen Presentation The process by which antigen is presented to lymphocytes in a form they can recognize. This is performed by antigen presenting cells (APCs). Some antigens require processing before they can be recognized. Antigen processing consists of ingestion and partial digestion of the antigen by the APC, followed by presentation of fragments on the cell surface. (From Rosen et al., Dictionary of Immunology, 1989) Antigen Processing,Antigen Presentations,Antigen Processings

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