Kuo S C, Hammer D A, Lauffenburger D A
Department of Chemical Engineering, University of Illinois at Urbana-Champaign 61801, USA.
Biophys J. 1997 Jul;73(1):517-31. doi: 10.1016/S0006-3495(97)78090-1.
The receptor-mediated adhesion of cells to ligand-coated surfaces is important in many physiological and biotechnological processes. Previously, we measured the detachment of antibody-coated spheres from counter-antibody- and protein A-coated substrates using a radial-flow detachment assay and were able to relate mechanical adhesion strength to chemical binding affinity (Kuo and Lauffenburger, Biophys. J. 65:2191-2200 (1993)). In this paper, we use "adhesive dynamics" to simulate the detachment of antibody-coated hard spheres from a ligand-coated substrate. We modeled the antibody-ligand (either counter-antibody or protein A) bonds as adhesive springs. In the simulation as in the experiments, beads attach to the substrate under static conditions. Flow is then initiated, and detachment is measured by the significant displacement of previously bound particles. The model can simulate the effects of many parameters on cell detachment, including hydrodynamic stresses, receptor number, ligand density, reaction rates between receptor and ligand, and stiffness and reactive compliance of the adhesive springs. The simulations are compared with experimental detachment data, thus relating measured bead adhesion strength to molecular properties of the adhesion molecules. The simulations accurately recreated the logarithmic dependence of adhesion strength on affinity of receptor-ligand recognition, which was seen in experiments and predicted by analytic theory. In addition, we find the value of the reactive compliance, the parameter which relates the strain of a bond to its rate of breakage, that gives the best match between theory and experiment to be 0.01. Finally, we analyzed the effect of varying either the forward or reverse rate constants as different ways to achieve the same affinity, and showed that adhesion strength depends uniquely on the equilibrium affinity, not on the kinetics of binding. Given that attachment is independent of affinity, detachment and attachment are distinct adhesive phenomena.
细胞与配体包被表面的受体介导黏附在许多生理和生物技术过程中都很重要。此前，我们使用径向流分离测定法测量了抗体包被的球体从抗抗体和蛋白A包被的底物上的分离，并能够将机械黏附强度与化学结合亲和力联系起来（Kuo和Lauffenburger，《生物物理杂志》65:2191 - 2200 (1993)）。在本文中，我们使用“黏附动力学”来模拟抗体包被的硬球体从配体包被的底物上的分离。我们将抗体 - 配体（抗抗体或蛋白A）键模拟为黏附弹簧。在模拟中，如同在实验中一样，珠子在静态条件下附着到底物上。然后启动流动，并通过先前结合的颗粒的显著位移来测量分离。该模型可以模拟许多参数对细胞分离的影响，包括流体动力应力、受体数量、配体密度、受体与配体之间的反应速率以及黏附弹簧的刚度和反应柔顺性。将模拟结果与实验分离数据进行比较，从而将测得的珠子黏附强度与黏附分子的分子特性联系起来。模拟准确地重现了黏附强度对受体 - 配体识别亲和力的对数依赖性，这在实验中观察到并由解析理论预测。此外，我们发现反应柔顺性的值，即一个将键的应变与其断裂速率联系起来的参数，在理论与实验之间给出最佳匹配的值为0.01。最后，我们分析了改变正向或反向速率常数作为实现相同亲和力的不同方式的影响，并表明黏附强度仅取决于平衡亲和力，而不取决于结合动力学。鉴于附着与亲和力无关，分离和附着是不同的黏附现象。
