Analysis of the allele specific Ag-binding site on murine class II MHC
Kajino, K.
Hokkaido Journal of Medical Science 71(2): 187-203
1996
ISSN/ISBN: 0367-6102 PMID: 8641675 Document Number: 467342
Residues 46 and 54 on pigeon cytochrome c 43 58 (p43-58) analogues function as agretopes (sites bound to MHC molecules). Phenylalanine (F) and alanine (A) at positions 46 and 54 on p43-58 respectively bind to I-A-b. Aspartic acid (D) and alanine at positions 46 and 54 respectively bind to I-A-b. To determine the allele specific binding sites (desetope (s)) on class 11 molecules that are correspondent to the agretopes of peptide antigen (Ag), we analyzed directly binding capacity of p43-58 analogues with glutamic acid (E) at the epitopic position 50 (50E) to L cell transfectants expressing recombinant I-A molecules between b and k types. An A-k binding peptide, 46D50E54A, bound to transfectants possessing amino acid sequence of k type on N-terminal half of alpha-helix of A-alpha-chain irrespective of the b type sequence on the other part, whereas an A-b binding peptide, 46F50E54A, did not bind to these transfectants. Thus, agretopic residue 46 of 46D50E54A and 46F50E54A peptides appeared to bind to N-terminal half of alpha-helix of A-alpha-chain. To define critical residues for the allele specific peptide binding, we then analyzed peptide binding capacity of A-k mutants substituted one of four polymorphic residues between A-k and A-b molecules. An A-k mutant, A-k-alpha(56A), where arginine (R) at position 56 of the A-k-alpha-chains was substituted with alanine located at the same position 56 of the A-b-alpha-chains hardly bound 46D50E54A. By contrast, the A-k-alpha(56A) bound 46F50E54A. Furthermore, A-k restricted T cell hybridomas responded to 46F50E54A but not to 46D50E54A in the presence of the A-k-alpha(56A) APC. Thus, an amino acid on the position 56 of A-alpha-chain determines critically specificity of the allele specific peptide binding (desetope).