title: The invariant chain derived fragment CLIP is an efficient in vitro inhibitor of peptide binding to MHC class II molecules.
abstract: The invariant chain derived peptide CLIP inhibits association of peptides to the class II peptide binding site. Two DR3 specific peptides, the microbacterial heat shock protein 65 derived peptide hsp3-13 and the naturally occurring invariant chain derived peptide Ii131-149 were employed to study binding inhibition by CLIP (Ii82-102) in a series of combinations. Incubation of detergent solubilized DR polypeptides from Ii-free cells with 500 microM of synthetic CLIP almost completely prevents binding of 50 microM subsequently added DR3-specific peptides. When CLIP and the peptides were added simultaneously to DR3 molecules, binding of hsp3-13 was abolished, whereas binding of Ii131-149 was only partially blocked. This indicates apparent affinity differences of the peptides. The addition of CLIP to preformed DR-peptide complexes substantially reduced binding of hsp3-13,while there was little effect on the DR associated Ii131-149. The profound inhibitory ability of CLIP, which in vivo would diminish binding of antigenic peptides, suggests an intracellular mechanism that abrogates the persistence of the CLIP-DR complex. The HLA-DM molecules have been suggested as candidates for this function. The strong in vitro binding of the naturally occurring peptide Ii131-149 to DR3 may suggest that only limited amounts of this peptide are available in vivo for competition of exogenous peptide binding to class II molecules.
authors.affiliation: Section of Immunobiology, Institute of Zoology, University of Bonn, Bonn, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Hitzel
authors.forename: N
authors.initials: N
authors.lastname: Koch
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins; D001667:Binding, Competitive; D002460:Cell Line; D018834:Chaperonin 60; D018833:Chaperonins / Q000737:chemistry / Q000276:immunology; D015803:HLA-DR3 Antigen / Q000378:metabolism*; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010455:Peptides / Q000276:immunology / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D014162:Transfection
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D001426:Bacterial Proteins; D018834:Chaperonin 60; D015803:HLA-DR3 Antigen; D000949:Histocompatibility Antigens Class II; D010455:Peptides; C074119:heat-shock protein 65, Mycobacterium; C045084:invariant chain; D018833:Chaperonins