期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：36
页码：13114-13120
DOI：10.1073/pnas.0404201101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Abciximab, a derivative of the murine mAb 7E3, protects against ischemic complications of percutaneous coronary interventions by inhibiting ligand binding to the {alpha}IIb{beta}3 receptor. In this study we identified regions on integrin {beta}3 that control 7E3 binding. Murine/human amino acid substitutions were created in two regions of the {beta}A domain that previous studies found to influence 7E3 binding: the C177-C184 loop and K125-N133. The T182N substitution and a K125Q mutation reduced 7E3 binding to human {beta}3 in complex with {alpha}IIb. The introduction of both the human C177-C184 region and human W129 into murine {beta}3 was necessary and sufficient to permit 7E3 binding to the human {alpha}IIb/murine {beta}3 complex. Although we cannot exclude allosteric effects, we propose that 7E3 binds between C177-C184 and W129, which are within 15 A of each other in the crystal structure and close to the {beta}3 metal ion-dependent adhesion site. We previously demonstrated that 7E3 binds more rapidly to activated than unactivated platelets. Because it has been proposed that {alpha}IIb{beta}3 changes from a bent to an extended conformation upon activation, we hypothesized that 7E3 binds less well to the bent than the extended conformation. In support of this hypothesis we found that 7E3 bound less well to an {alpha}IIb{beta}3 construct locked in a bent conformation, and unlocking the conformation restored 7E3 binding. Thus, our data are consistent with {alpha}IIb{beta}3 existing in variably bent conformations in equilibrium with each other on unactivated platelets, and activation resulting in {alpha}IIb{beta}3 adopting a more extended conformation.
