Energy landscapes of receptor-ligand bonds explored with dynamic force spectroscopy
Energy landscapes of receptor-ligand bonds explored with dynamic force spectroscopy
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作者：
Merkel, R;Nassoy, P;Evans, E
原子力显微镜(AFM)(1，2)被用来测量生物受体分子与其配体(3-6)之间的键强度。但对于弱的非共价键，随着加载速率的改变，预测了键强度的动态谱，所测得的强度由力驱动的键解离路径(7)在能量图中穿过的显著势垒所支配。换句话说，开创性的早期原子力显微镜测量只代表了连续的键强度谱中的一个点，因为理论预测这些强度将取决于施加载荷的速度。在这里，我们报告了链霉亲和素(或亲和素)和生物素(8)之间的键的强度谱，生物素(8)是早期AFM研究中使用的受体-配体相互作用的原型(3-5)，并已被分子动力学模拟(9，10)。我们探索了六个数量级以上的键形成，发现在这个范围内，随着加载速率的增加，键的存活时间从大约1min缩短到0.001 S。同时，键合强度从约5pN增加到170pN。因此，尽管它们是生物学上最强的非共价键之一(亲和力为10(13)到10(15)M-1)(8，11)，但这些键实际上看起来很强或很弱，这取决于它们被加载的速度。我们还能够将来自我们的强度光谱的激活势垒与来自生物素-亲和素复合体的模拟得到的能量景观的形状联系起来。
Atomic force microscopy (AFM)(1,2) has been used to measure the strength of bonds between biological receptor molecules and their ligands(3-6). But for weak noncovalent bonds, a dynamic spectrum of bond strengths is predicted as the loading rate is altered, with the measured strength being governed by the prominent barriers traversed in the energy landscape along the force-driven bond-dissociation pathway(7). In other words, the pioneering early AFM measurements represent only a single point in a continuous spectrum of bond strengths, because theory predicts that these will depend on the rate at which the load is applied. Here we report the strength spectra for the bonds between streptavidin (or avidin) and biotin(8)-the prototype of receptor-ligand interactions used in earlier AFM studies(3-5), and which have been modelled by molecular dynamics(9,10). We have probed bond formation over six orders of magnitude in loading rate, and find that the bond survival time diminished from about 1 min to 0.001 s with increasing loading rate over this range. The bond strength, meanwhile, increased from about 5 pN to 170 pN. Thus, although they are among the strongest noncovalent linkages in biology (affinity of 10(13) to 10(15) M-1)(8,11), these bonds in fact appear strong or weak depending on how fast they are loaded. We are also able to relate the activation barriers derived from our strength spectra to the shape of the energy landscape derived from simulations of the biotin-avidin complex.