Kontou M, Leonidas D D, Vatzaki E H, Tsantili P, Mamalaki A, Oikonomakos N G, Acharya K R, Tzartos S J
Department of Biochemistry, Hellenic Pasteur Institute, Athens, Greece.
Eur J Biochem. 2000 Apr;267(8):2389-97. doi: 10.1046/j.1432-1327.2000.01252.x.
The crystal structure of the Fab fragment of a rat monoclonal antibody, number 192, with a very high affinity (Kd = 0.05 nM) for the main immunogenic region of the human muscle acetylcholine receptor (AChR), has been determined and refined to 2.4 A resolution by X-ray crystallographic methods. The overall structure is similar to a Fab (NC6.8) from a murine antibody, used as a search model in molecular replacement. Structural comparisons with known antibody structures showed that the conformations of the hypervariable regions H1, H2, L1, L2, L3 of Fab192 adopt the canonical structures 1, 1, 2, 1, and 1, respectively. The surface of the antigen-binding site is relatively planar, as expected for an antibody against a large protein antigen, with an accessible area of 2865 A2. Analysis of the electrostatic surface potential of the antigen-binding site shows that the bottom of the cleft formed in the center of the site appears to be negatively charged. The structure will be useful in the rational design of very high affinity humanized mutants of Fab192, appropriate for therapeutic approaches of the model autoimmune disease myasthenia gravis.
已通过X射线晶体学方法确定并精修了一种大鼠单克隆抗体（编号192）Fab片段的晶体结构，该抗体对人肌肉乙酰胆碱受体（AChR）的主要免疫原性区域具有非常高的亲和力（Kd = 0.05 nM），分辨率达到2.4 Å。其整体结构与一种鼠源抗体的Fab（NC6.8）相似，后者用作分子置换中的搜索模型。与已知抗体结构的比较表明，Fab192的高变区H1、H2、L1、L2、L3的构象分别采用典型结构1、1、2、1和1。抗原结合位点的表面相对平坦，这对于针对大蛋白抗原的抗体而言是预期的，其可及面积为2865 Å2。对抗原结合位点静电表面电位的分析表明，在该位点中心形成的裂隙底部似乎带负电荷。该结构将有助于对Fab192进行非常高亲和力的人源化突变体的合理设计，适用于自身免疫性疾病重症肌无力模型的治疗方法。
