Donhauser Zachary J, Saunders Jared T, D'Urso Dennis S, Garrett Teresa A
Department of Chemistry, Vassar College , Poughkeepsie, New York 12601, United States.
Biochemistry. 2017 Nov 7;56(44):5900-5909. doi: 10.1021/acs.biochem.7b00653.
Tau is a microtubule-associated protein found in neuronal axons that has several well-known functions, such as promoting microtubule polymerization, stabilizing microtubules against depolymerization, and spatially organizing microtubules in axons. Two contrasting models have been previously described to explain tau's ability to organize the spacing between microtubules: complementary dimerization of the projection domains of taus on adjacent microtubules or tau's projection domain acting as a polyelectrolyte brush. In this study, atomic force microscopy was used to interrogate intermolecular interactions between layers of tau protein immobilized on mica substrates and on silicon nitride atomic force microscope tips. On these surfaces, tau adopts an orientation comparable to that when bound to microtubules, with the basic microtubule binding domain immobilized and the acidic domains extending into solution. Force-distance curves collected via atomic force microscopy reveal that full length human tau, when assembled into dense surface-bound layers, can participate in attractive electrostatic interactions consistent with the previously reported dimerization model. However, modulating the ionic strength of the surrounding solution can change the structure of these layers to produce purely repulsive interactions consistent with a polyelectrolyte brush structure, thus providing biophysical evidence to support both the zipper and brush models. In addition, a pair of projection domain deletion mutants were examined to investigate whether the projection domain of the protein is essential for the dimerization and brush models. Force-distance curves collected on layers of these proteins demonstrate that the C-terminus can play a role analogous to that of the projection domain.
Tau是一种在神经元轴突中发现的微管相关蛋白，具有多种众所周知的功能，如促进微管聚合、稳定微管防止解聚以及在轴突中对微管进行空间组织。先前已经描述了两种截然不同的模型来解释tau组织微管间距的能力：相邻微管上tau投影结构域的互补二聚化或tau的投影结构域充当聚电解质刷。在本研究中，使用原子力显微镜来研究固定在云母基板和氮化硅原子力显微镜尖端上的tau蛋白层之间的分子间相互作用。在这些表面上，tau采取的取向与结合到微管时的取向相当，基本的微管结合结构域固定，酸性结构域延伸到溶液中。通过原子力显微镜收集的力-距离曲线表明，全长人tau在组装成致密的表面结合层时，可以参与与先前报道的二聚化模型一致的有吸引力的静电相互作用。然而，调节周围溶液的离子强度可以改变这些层的结构，以产生与聚电解质刷结构一致的纯粹排斥相互作用，从而提供生物物理证据来支持拉链模型和刷模型。此外，研究了一对投影结构域缺失突变体，以研究该蛋白的投影结构域对于二聚化模型和刷模型是否必不可少。在这些蛋白质层上收集的力-距离曲线表明，C末端可以发挥与投影结构域类似的作用。
