Papadouli I, Potamianos S, Hadjidakis I, Bairaktari E, Tsikaris V, Sakarellos C, Cung M T, Marraud M, Tzartos S J
Hellenic Pasteur Institute, Athens, Greece.
Biochem J. 1990 Jul 1;269(1):239-45. doi: 10.1042/bj2690239.
The target of most of the autoantibodies against the acetylcholine receptor (AChR) in myasthenic sera is the main immunogenic region (MIR) on the extracellular side of the AChR alpha-subunit. Binding of anti-MIR monoclonal antibodies (mAbs) has been recently localized between residues alpha 67 and alpha 76 of Torpedo californica electric organ (WNPADYGGIK) and human muscle (WNPDDYGGVK) AChR. In order to evaluate the contribution of each residue to the antigenicity of the MIR, we synthesized peptides corresponding to residues alpha 67-76 from Torpedo and human AChRs, together with 13 peptide analogues. Nine of these analogues had one residue of the Torpedo decapeptide replaced by L-alanine, three had a structure which was intermediate between those of the Torpedo and human alpha 67-76 decapeptides, and one had D-alanine in position 73. Binding studies employing six anti-MIR mAbs and all 15 peptides revealed that some residues (Asn68 and Asp71) are indispensable for binding by all mAbs tested, whereas others are important only for binding by some mAbs. Antibody binding was mainly restricted to residues alpha 68-74, the most critical sequence being alpha 68-71. Fish electric organ and human MIR form two distinct groups of strongly overlapping epitopes. Some peptide analogues enhanced mAb binding compared with Torpedo and human peptides, suggesting that the construction of a very antigenic MIR is feasible.
重症肌无力患者血清中大多数抗乙酰胆碱受体（AChR）自身抗体的靶标是AChRα亚基胞外侧的主要免疫原性区域（MIR）。抗MIR单克隆抗体（mAb）的结合位点最近已定位在加州电鳐电器官（WNPADYGGIK）和人肌肉（WNPDDYGGVK）AChR的α67和α76残基之间。为了评估每个残基对MIR抗原性的贡献，我们合成了与来自电鳐和人AChR的α67 - 76残基相对应的肽段，以及13种肽类似物。其中9种类似物将电鳐十肽中的一个残基替换为L - 丙氨酸，3种具有介于电鳐和人α67 - 76十肽结构之间的结构，还有一种在73位含有D - 丙氨酸。使用6种抗MIR mAb和所有15种肽进行的结合研究表明，一些残基（Asn68和Asp71）对于所有测试的mAb结合都是不可或缺的，而其他残基仅对某些mAb的结合很重要。抗体结合主要局限于α68 - 74残基，最关键的序列是α68 - 71。鱼电器官和人MIR形成两组明显不同但有大量重叠的表位。与电鳐和人肽相比，一些肽类似物增强了mAb结合，这表明构建一个极具抗原性的MIR是可行的。
