Quarsten H, Paulsen G, Johansen B H, Thorpe C J, Holm A, Buus S, Sollid L M
Institute of Transplantation Immunology, Rikshospitalet, University of Oslo, Norway.
Int Immunol. 1998 Aug;10(8):1229-36. doi: 10.1093/intimm/10.8.1229.
Susceptibility and resistance to type 1 diabetes are associated with MHC class II alleles that carry non-Asp and Asp at residue 57 of their beta chain respectively. The effect of Asp or non-Aspbeta57 may relate to a differential ability of distinct class II molecules to bind specific immuno-pathogenic peptides. Recent studies in man and mouse have revealed that some type 1 diabetes-predisposing non-Aspbeta57 class II molecules (i.e. DQ8, DR4Dw15 and I-Ag7) preferentially bind peptides with a negatively charged anchor residue at P9. It has been suggested that this is a common feature of type 1 diabetes-predisposing class II molecules. The molecular explanation for such a phenomenon could be that class II beta chains with Aspbeta57 form a salt bridge between Aspbeta57 and a conserved Arg of the a chain, whereas in non-Aspbeta57 molecules the Arg is unopposed and free to interact with negatively charged P9 peptide anchor residues. We have investigated the specificity of the P9 pocket of the type 1 diabetes-associated DQ2 molecule and in particular examined for charge effects at this anchor position. Different approaches were undertaken. We analyzed binding of a high-affinity binding ligand and P9-substituted variants of this peptide, and we analyzed the binding of a set of synthetic random peptide libraries. The binding analyses were performed with wild-type DQ2 and a mutated DQ2 with Ala at beta57 substituted with Asp. Our results indicate that the wild-type DQ2 (non-Aspbeta57) prefers large hydrophobic residues at P9 and that there is no particular preference for binding peptides with negatively charged residues at this position. The specificity of the P9 pocket in the mutated DQ molecule is altered, indicating that the beta57 residue contributes to determining the specificity of the P9 pocket. Our data do not lend support to the hypothesis that all non-Asp beta57 class II molecules predispose to development of disease by binding peptides with negatively charged P9 anchor residues.
1型糖尿病的易感性和抗性分别与MHC II类等位基因相关，这些等位基因的β链第57位残基携带非天冬氨酸（non-Asp）和天冬氨酸（Asp）。Asp或non-Aspβ57的作用可能与不同的II类分子结合特定免疫致病肽的能力差异有关。最近在人和小鼠中的研究表明，一些1型糖尿病易感的non-Aspβ57 II类分子（即DQ8、DR4Dw15和I-Ag7）优先结合在P9位带有负电荷锚定残基的肽段。有人提出这是1型糖尿病易感II类分子的一个共同特征。这种现象的分子解释可能是，带有Aspβ57的II类β链在Aspβ57和α链的一个保守精氨酸之间形成盐桥，而在non-Aspβ57分子中，精氨酸没有与之配对的基团，可自由与带负电荷的P9肽锚定残基相互作用。我们研究了1型糖尿病相关DQ2分子P9口袋的特异性，特别考察了该锚定位点的电荷效应。我们采用了不同的方法。我们分析了一种高亲和力结合配体及其P9取代变体的结合情况，还分析了一组合成随机肽库的结合情况。结合分析使用野生型DQ2和β57位丙氨酸被天冬氨酸取代的突变型DQ2进行。我们的结果表明，野生型DQ2（non-Aspβ57）在P9位更喜欢大的疏水残基，并且在该位置结合带负电荷残基的肽段没有特别偏好。突变型DQ分子中P9口袋的特异性发生了改变，这表明β57残基有助于确定P9口袋的特异性。我们的数据不支持这样的假说，即所有non-Aspβ57 II类分子都通过结合带有负电荷P9锚定残基的肽段而导致疾病发生。
