Tropomyosin-regulated actomyosin-based contractility in nonmuscles cells

我们的目标是阐明原肌球蛋白调节非肌肉细胞基于肌球蛋白的收缩的机制。原肌球蛋白与裸肌动蛋白细丝的结合被描述为格式塔结合的概念。然而，格式塔结合很容易被其他肌动蛋白结合蛋白破坏，并且不能很好地解释原肌球蛋白的低分子亚型在功能不同的细丝群形成中的作用，这些细丝群显示出明确的异构体组成和功能。我们的工作是基于一个模型，在该模型中，除了胞浆肌动蛋白和TM亚型外，还需要NM-2亚型来建立具有明确定义的属性的最小功能实体。肌球蛋白在产生的ATmM复合体中介导所有立体特异性的相互作用，从而增强在人类细胞中共存的单个肌动蛋白、肌球蛋白和原肌球蛋白异构体之间相互作用的特异性。肌球蛋白与肌动蛋白的依赖于ATP的循环相互作用以及作用力和运动的产生支持了结构上不同的细丝群体的形成。此外，我们推测，肌球蛋白马达活动增强了由此产生的细丝群体的动态性质，增强了它们履行特定功能角色的能力，以及它们在细胞不同区域的独立调节。数以千计的剪接异构体和突变体的潜在组合是执行这一项目的一个特别挑战。基于我们的初步工作，似乎用相对较少的亚型组合的研究足以对在人类细胞中发现的最常见的ATmM复合体做出准确的预测。原型细胞骨架复合体的个体速率和平衡常数的可用性将极大地推动该领域的发展，因为目前的建模方法基于对骨骼肌α-肌动蛋白进行的少量研究是相当不准确的。原型ATmM复合体的重组和详细的结构特征有望揭示定义TM调节的基于肌动球蛋白的收缩、膜成形和重塑以及细胞信号事件整合的结构-功能关系的密码的洞察力。

Our goal is the elucidation of mechanisms that govern tropomyosin-regulated actomyosin-based contractility in nonmuscle cells. Tropomyosin-binding to bare actin filaments has been described with the notion gestalt-binding. However, gestalt-binding is easily disrupted by other actin-binding proteins and fails to provide a satisfactory explanation for the role of low molecular weight isoforms of tropomyosin in the formation of functionally distinct filament populations, which display well-defined isoform-composition and function. Our work is based on a model where NM-2 isoforms are required in addition to cytosolic actin and Tm isoforms to establish minimal functional entities with clearly defined properties. Myosin mediates all stereospecific interactions in the resulting ATmM complex, thereby enhancing the specificity of interactions between the individual actin, myosin, and tropomyosin isoforms that coexist in the human cells. The cyclic ATP-dependent interaction of myosin with actin and the production of force and movement support the formation of structurally distinct filament populations. Moreover, we presume that myosin motor activity enhances the dynamic nature of the resulting filament populations, their ability to fulfill a specific functional role, and their independent regulation in different regions of the cell. The thousands of potential combinations of splice isoforms and mutants are a particular challenge in performing this project. Based on our preliminary work, it appears likely that studies with a relatively small number of isoform combinations are sufficient to make accurate predictions about the most common ATmM complexes found in human cells. The availability of the individual rate and equilibrium constants for prototypic cytoskeletal complexes will greatly advance the field, as current modeling approaches are rather inaccurately based on a small number of studies performed with skeletal muscle alpha-actin. Reconstitution and detailed structural characterization of prototypic ATmM complexes promises to reveal insights in the code that defines structure-function relationships in Tm-regulated actomyosin-based contraction, membrane shaping and remodeling, and the integration of cellular signaling events.