Husson Julien, Pincet Frédéric
Laboratoire de Physique Statistique de l'Ecole Normale Supérieure, Associé aux Universités Paris 6 et Paris 7, UMR CNRS 8550, 24 Rue Lhomond, 75231 Paris Cedex 05, France.
Phys Rev E Stat Nonlin Soft Matter Phys. 2008 Feb;77(2 Pt 2):026108. doi: 10.1103/PhysRevE.77.026108. Epub 2008 Feb 14.
Experimentalists who measure the rupture force of a single molecular bond usually pull on that bond at a constant speed, keeping the loading rate r=df/dt constant. The challenge is to extract the energy landscape of the interaction between the two molecules involved from the experimental rupture force distribution under several loading rates. This analysis requires the use of a model for the shape of this energy landscape. Several barriers can compose the landscape, though molecular bonds with a single barrier are often observed. The Bell model is commonly used for the analysis of rupture force measurements with bonds displaying a single barrier. It provides an analytical expression of the most likely rupture force which makes it very simple to use. However, in principle, it can only be applied to landscapes with extrema whose positions do not vary under force. Here, we evaluate the general relevance of the Bell model by comparing it with another analytical model for which the landscape is harmonic in the vicinity of its extrema. Similar shapes of force distributions are obtained with both models, making it difficult to confirm the validity of the Bell model for a given set of experimental data. Nevertheless, we show that the analysis of rupture force experiments on such harmonic landscapes with the Bell model provides excellent results in most cases. However, numerical computation of the distributions of the rupture forces on piecewise-linear energy landscapes indicates that the blind use of any model such as the Bell model may be risky, since there often exist several landscapes compatible with a given set of experimental data. Finally, we derive a universal relation between the range and energy of the bond and the force spectrum. This relation does not depend on the shape of the energy landscape and can thus be used to characterize unambiguously any one-barrier landscape from experiments. All the results are illustrated with the streptavidin-biotin bond.
测量单个分子键断裂力的实验人员通常以恒定速度拉动该键，使加载速率r = df/dt保持恒定。挑战在于从几种加载速率下的实验断裂力分布中提取所涉及的两个分子之间相互作用的能量态势。这种分析需要使用一个关于这种能量态势形状的模型。能量态势可能由多个势垒组成，不过经常观察到具有单个势垒的分子键。贝尔模型通常用于分析具有单个势垒的键的断裂力测量。它提供了最可能断裂力的解析表达式，使用起来非常简单。然而，原则上它只能应用于其极值位置在受力时不变的态势。在这里，我们通过将贝尔模型与另一个解析模型进行比较来评估其普遍适用性，对于后一个模型，其态势在极值附近是简谐的。两个模型得到的力分布形状相似，这使得难以确定贝尔模型对于给定一组实验数据的有效性。尽管如此，我们表明在大多数情况下，用贝尔模型分析这种简谐态势下的断裂力实验能得到很好的结果。然而，对分段线性能量态势上断裂力分布的数值计算表明，盲目使用任何模型（如贝尔模型）可能存在风险，因为通常存在几种与给定一组实验数据兼容的态势。最后，我们推导出键的范围和能量与力谱之间的普遍关系。这种关系不依赖于能量态势的形状，因此可用于从实验中明确地表征任何一个势垒的态势。所有结果都以链霉亲和素 - 生物素键为例进行了说明。
