title: Immunological significances of invariant chain from the aspect of its structural homology with the cystatin family.
abstract: The primary structure of p31 of invariant chain (Ii-chain) shows about 50% homology with those of the cystatin family which are endogenous cysteine protease inhibitors. The binding domains between Ii-chain and HLA-DR-7 were estimated from the structural homology between cystatin and Ii-chain and also between cathepsins and DR-7, respectively. The QL64-71 and GS76-88 of Ii-chain were estimated to be the binding domains with GG45-51 and VS57-63 of HLA-DR7, respectively. The purified human Ii-chain from spleen is capable of forming four molecular forms from monomer to tetramer by redox-potential dependent disulfide bond formation. The Ii-chain inhibits cathepsin L and H competitively as a dimer and the K(i) value for cathepsin L was 4.1 x 10(-8) M, but cathepsin B was not inhibited at all. The Ii-chain showed mainly a dimer (60 kDa) under the assay condition of cathepsins with cysteine and was not degraded by these cathepsins. The Ii-chain may play an important role in the regulation of antigenic peptide presentation to MHC class II.
authors.affiliation: Institute for Health Sciences, Tokushima Bunri University, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Katunuma
authors.forename: H
authors.initials: H
authors.lastname: Kakegawa
authors.forename: Y
authors.initials: Y
authors.lastname: Matsunaga
authors.forename: T
authors.initials: T
authors.lastname: Saibara
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte; D001665:Binding Sites; D002403:Cathepsins / Q000378:metabolism; D015891:Cystatins / Q000737:chemistry* / Q000276:immunology; D006684:HLA-DR Antigens / Q000737:chemistry; D000949:Histocompatibility Antigens Class II / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013154:Spleen / Q000737:chemistry
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D015891:Cystatins; D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II; C045084:invariant chain; D002403:Cathepsins