Nonlinear viscoelasticity of actin transiently cross-linked with mutant α-actinin-4.
Nonlinear viscoelasticity of actin transiently cross-linked with mutant α-actinin-4.
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DOI：
10.1016/j.jmb.2011.06.049
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发表时间：
2011-09-02
影响因子：
5.6
通讯作者：
Weitz DA
中科院分区：
文献类型：
--
作者：
Yao NY;Becker DJ;Broedersz CP;Depken M;Mackintosh FC;Pollak MR;Weitz DA
丝状肌动蛋白和相关的肌动蛋白结合蛋白在真核细胞的力学特性中起着重要的作用。它们也可以在疾病中发挥关键作用;例如，α-辅肌动蛋白-4（Actn 4）（一种动态肌动蛋白交联蛋白）的突变会导致人类和小鼠的蛋白尿疾病。氨基酸取代强烈影响Actn 4的结合亲和力和蛋白质结构。为了研究这种取代对细胞骨架网络的物理影响，我们研究了与野生型和突变型α-辅肌动蛋白-4交联的体外肌动蛋白网络的整体力学行为。这些网络表现出复杂的粘弹性响应，其特征在于在最长的时间尺度上的流体状行为，这一特征可以通过动态交联模型定量地解释。网络的弹性行为是高度非线性的，随着施加的应力而变得更硬。这种非线性弹性响应对α-辅肌动蛋白-4的突变也高度敏感;特别是，我们观察到与携带致病K255 E突变的Actn 4交联的肌动蛋白网络与与野生型Actn 4交联的网络相比更脆，断裂应力更低。此外，切除Actn 4中第一个肌动蛋白结合位点（ABS 1）的突变消除了网络的应激能力。与突变型Actn 4交联的肌动蛋白网络的机械性质的这些变化可能代表遗传性局灶节段性肾小球硬化症的潜在疾病机制的物理决定因素。
Filamentous actin and associated actin binding proteins play an essential role in governing the mechanical properties of eukaryotic cells. They can also play a critical role in disease; for example, mutations in α-actinin-4 (Actn4), a dynamic actin cross-linking protein, cause proteinuric disease in humans and mice. Amino acid substitutions strongly affect the binding affinity and protein structure of Actn4. To study the physical impact of such substitutions on the underlying cytoskeletal network, we examine the bulk-mechanical behavior of in vitro actin networks cross-linked with wild type and mutant α-actinin-4. These networks exhibit a complex viscoelastic response and are characterized by fluid-like behavior at the longest time scales, a feature which can be quantitatively accounted for through a model governed by dynamic cross-linking. The elastic behavior of the network is highly nonlinear, becoming much stiffer with applied stress. This nonlinear elastic response is also highly sensitive to the mutations of α-actinin-4; in particular, we observe that actin networks cross-linked with Actn4 bearing the disease causing K255E mutation are more brittle with a lower breaking stress in comparison to networks cross-linked with wild-type Actn4. Furthermore, a mutation that ablates the first actin binding site (ABS1) in Actn4 abrogates the network’s ability to stress-stiffen. These changes in the mechanical properties of actin networks cross-linked with mutant Actn4 may represent physical determinants of the underlying disease mechanism in inherited focal segmental glomerulosclerosis.