Molecular mechanisms of bundled actin structure assembly by formins

项目总结 细胞动态组装一组不同的基于肌动蛋白的结构，以执行必要的过程，包括 运动、分裂和信号传递。一类肌动蛋白结构由肌动蛋白细丝网络组成，这些网络 捆绑在一起形成并行或反并行体系结构。这些捆绑的肌动蛋白结构包括收缩 环、肌动蛋白缆索、丝状伪足和促进局灶性黏附成熟和核的应力纤维 定位。组成这些结构的肌动蛋白细丝主要由福尔马林聚合，福尔马林是一族 成核并引导未分枝的肌动蛋白细丝伸长的蛋白质。哺乳动物表达15种形成蛋白 异构体，每一种都具有独特的肌动蛋白组装属性，并在细胞中扮演特定的角色。 尽管福尔曼基因的突变与包括白血病前期在内的许多人类疾病有关 疾病和癌症，目前还不清楚每种福尔敏异构体的聚合活性是如何调节的 一种特定的捆绑肌动蛋白结构的组装，并参与特定的细胞过程。为了弥合这一点 理解上的差距，我们必须确定福尔马林如何在捆绑肌动蛋白结构的背景下发挥作用 存在于细胞中。我们将通过描述福尔明介导的组装机制来解决这个问题 捆绑的肌动蛋白结构。我们的中心假设是将Forin结合的肌动蛋白细丝掺入到 束状结构通过使福尔马林受力、丝束和细丝来调节聚合 断绝关系。我们将结合使用生物物理学和细胞生物学的方法来验证这一假说 追求三个具体目标：(1)阐明力对Form in介导的机制的影响 长丝伸长，(2)研究长丝捆扎与甲醛聚合的关系 活性，以及(3)评估细丝周转对捆绑肌动蛋白结构组装的贡献。通过 建立福尔明导向的捆绑肌动蛋白组装机制，我们将获得对 由福尔马林调节的大量细胞过程。这项工作还将提供一个分子基础 了解福尔马林如何促进细胞的健康增殖和正常发育。

PROJECT SUMMARY Cells dynamically assemble a diverse set of actin-based structures to perform essential processes including motility, division and signaling. One class of actin structures consists of networks of actin filaments that are bundled together into parallel or anti-parallel architectures. These bundled actin structures include contractile rings, actin cables, filopodia, and the stress fibers that promote focal adhesion maturation and nuclear positioning. The actin filaments that comprise these structures are primarily polymerized by formins, a family of proteins that nucleate and direct the elongation of unbranched actin filaments. Mammals express 15 formin isoforms, each of which possesses unique actin assembly properties and plays a specific role in cells. Although mutations in formin genes are associated with a number of human diseases including preleukemic disorders and cancer, it remains unknown how the polymerization activity of each formin isoform is tuned for the assembly of a specific bundled actin structure and participation in a specific cellular process. To bridge this gap in understanding, we must establish how formins function in the context of the bundled actin structures that exist in cells. We will address this question by characterizing the mechanism of formin-mediated assembly of bundled actin structures. Our central hypothesis is that incorporation of formin-bound actin filaments into bundled structures modulates polymerization by exposing formins to force, filament bundling and filament severing. We will use a combination of biophysical and cell biological approaches to test this hypothesis by pursuing three specific aims: (1) To elucidate the effects of force on the mechanism of formin-mediated filament elongation, (2) to investigate the relationship between filament bundling and formin polymerization activity, and (3) to evaluate the contribution of filament turnover to bundled actin structure assembly. By establishing the mechanism of formin-directed bundled actin assembly, we will gain fundamental insights into the large number of cellular processes regulated by formins. This work will also provide a molecular basis for understanding how formins contribute to healthy cellular proliferation and normal development.