Farr Carol D, Tabet Michael R, Ball William J, Fishwild Dianne M, Wang Xia, Nair Anil C, Welsh William J
Center for Molecular Electronics, Department of Chemistry, University of Missouri-St. Louis, St. Louis, MO 63121, USA.
J Med Chem. 2002 Jul 18;45(15):3257-70. doi: 10.1021/jm0102811.
The present study indicates that the newly generated human sequence antidigoxin monoclonal antibody (mAb), 1B3, binds digoxin with a different fine specificity binding than our previously obtained human sequence monoclonal antibodies (mAbs) (Ball, W. J.; et al. J. Immunol. 1999, 163, 2291-2298). Uniquely, 1B3 has a higher affinity for digitoxin than digoxin, the immunizing hapten, and a strong requirement for at least one sugar residue linked to the aglycone (-genin). By means of comparative molecular field analysis (CoMFA), the results of competition binding studies for 56 cardiotonic and hormonal steroids were employed to develop three-dimensional quantitative structure-activity relationship (3D-QSAR) models for ligand binding to 1B3 and to three additional human sequence mAbs, as well as the murine antidigoxin mAb 40-50 (Mudgett-Hunter, M.; et al. Mol. Immunol. 1985, 22, 447-488). All five 3D-QSAR models yielded cross-validated q(2) values greater than 0.5, which indicates that they have significant predictive ability. The CoMFA StDevCoeff contour plots, as well as the competition results, indicate that 1B3 binds ligands in a manner distinct from the other four mAbs. The CoMFA contour plots for 40-50 were also compared with the known X-ray crystallographic structure of the 40-50-ouabain complex (Jeffrey, P. D.; et al. J. Mol. Biol. 1995, 248, 344-360) in order to identify correlations between residues in the mAb binding site and specific contour plot regions. These 3D-QSAR models and their respective contour plots should be useful tools to further understand the molecular nature of antibody-antigen interactions and to aid in the redesign or enhancement of therapeutic antibodies.
本研究表明，新产生的人源序列抗地高辛单克隆抗体（mAb）1B3与地高辛结合时具有与我们先前获得的人源序列单克隆抗体（mAbs）不同的精细特异性结合（Ball, W. J.等人，《免疫学杂志》，1999年，第163卷，第2291 - 2298页）。独特的是，1B3对洋地黄毒苷的亲和力高于免疫原性半抗原地高辛，并且强烈需要至少一个与苷元（-genin）相连的糖残基。通过比较分子场分析（CoMFA），利用56种强心和激素甾体的竞争结合研究结果，建立了配体与1B3以及另外三种人源序列mAb和鼠源抗地高辛mAb 40 - 50结合的三维定量构效关系（3D - QSAR）模型（Mudgett - Hunter, M.等人，《分子免疫学》，1985年，第22卷，第447 - 488页）。所有五个3D - QSAR模型的交叉验证q(2)值均大于0.5，这表明它们具有显著的预测能力。CoMFA标准偏差系数等高线图以及竞争结果表明，1B3以与其他四种mAb不同的方式结合配体。还将40 - 50的CoMFA等高线图与40 - 50 -哇巴因复合物的已知X射线晶体结构（Jeffrey, P. D.等人，《分子生物学杂志》，1995年，第248卷，第344 - 360页）进行了比较，以确定mAb结合位点中的残基与特定等高线图区域之间的相关性。这些3D - QSAR模型及其各自的等高线图应该是进一步理解抗体 - 抗原相互作用的分子本质以及辅助治疗性抗体重新设计或增强的有用工具。
