Immunological significances of invariant chain from the aspect of its structural homology with the cystatin family.
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.
Katunuma
N
N
Institute for Health Sciences, Tokushima Bunri University, Japan.
Kakegawa
H
H
Matsunaga
Y
Y
Saibara
T
T
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
D000944:Antigens, Differentiation, B-Lymphocyte; D015891:Cystatins; D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II; C045084:invariant chain; D002403:Cathepsins