Allele specificity of structural requirement for peptides bound to HLA-DRB1*0405 and -DRB1*0406 complexes: implication for the HLA-associated susceptibility to methimazole-induced insulin autoimmune syndrome.
Self-peptides bound to HLA-DR4 (DRA-DRB1*0405 complex) were eluted from the purified DR4 complex, fractionated on reverse-phase HPLC, and subjected to NH2-terminal sequencing. Seven independent sequences were obtained, and all putative peptides synthesized bound to DRB1*0405 as well as DRB1*0406 complex, which differ only at DR beta residues 37, 57, 74, and 86. Binding assay using analogue peptides of a DR4 binder GSTVFDNLPNPE revealed that FxxLxN is an important anchor motif necessary for binding (where x is any amino acid), which was common to DRB1*0405 and 0406. Determination of the binding affinity of 60 synthetic AAFAALANAA-based analogue peptides showed that substituting F to W or C; L to F, W, or Y; and N to Q or S on AAFAALANAA changed the affinity substantially between DRB1*0405 and DRB1*0406. It is noteworthy that all patients with methimazole-induced insulin autoimmune syndrome are positive for DRB1*0406 and negative for DRB1*0405. Interestingly, the quantitative structural motif identified in this study predicted that 8TSICSLYQLE17 of human insulin alpha chain may bind specifically to DRB1*0406 using its 10IxxLxQ15 motif. Indeed, DRB1*0406 complex bound 8TSICSLYQLE17 with a high affinity, and in striking contrast, DRB1*0405 complex did not. Furthermore, a short-term T cell line specific to human insulin established from a DRB1*0406-bearing individual did show reactivity with a peptide fragment containing the 10IxxLxQ15 motif. Although this fragment probably exists at a very low level under normal physiological conditions due to the disulfide bond between flanking cysteine residues (6Cys-11Cys), a reducing compound such as methimazole may cleave the disulfide bond in vivo and allow DR alpha-DRB1*0406 complex on antigen-presenting cells to bind much of the linear fragment of insulin alpha chain, which may lead to the activation of self-insulin-specific T-helper cells.
Matsushita
S
S
Department of Neuroscience and Immunology, Kumamoto University Graduate School of Medical Sciences, Japan.
Takahashi
K
K
Motoki
M
M
Komoriya
K
K
Ikagawa
S
S
Nishimura
Y
Y
D000483:Alleles; D000595:Amino Acid Sequence; D001327:Autoimmune Diseases / Q000209:etiology*; D001667:Binding, Competitive; D002460:Cell Line; D006684:HLA-DR Antigens / Q000737:chemistry / Q000378:metabolism*; D059811:HLA-DRB1 Chains; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000276:immunology*; D008213:Lymphocyte Activation; D008713:Methimazole / Q000009:adverse effects*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000302:isolation & purification / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology
D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; D000949:Histocompatibility Antigens Class II; D007328:Insulin; D010446:Peptide Fragments; D010455:Peptides; C019529:polyalanine; D008713:Methimazole