Smith Steven J, McCann Richard O
Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, 741 South Limestone Street, Lexington, Kentucky 40536-0509, USA.
Biochemistry. 2007 Sep 25;46(38):10886-98. doi: 10.1021/bi700637a. Epub 2007 Aug 28.
Focal adhesion complexes are plasma membrane-associated multicomponent complexes that are essential for integrin-linked signal transduction as well as cell adhesion and cell motility. The cytoskeletal protein Talin1 links integrin adhesion receptors with the actin cytoskeleton. Talin1 and the other animal and amoebozoan talins are members of the I/LWEQ module superfamily, which also includes fungal Sla2 and animal Hip1/Hip1R. The I/LWEQ module is a conserved C-terminal structural element that is critical for I/LWEQ module protein function. The I/LWEQ module of Talin1 binds to F-actin and targets the protein to focal adhesions in vivo. The I/LWEQ modules of Sla2 and Hip1 are required for the participation of these proteins in endocytosis. In addition to these roles in I/LWEQ module protein function, we have recently shown that the I/LWEQ module also contains a determinant for protein dimerization. Taken together, these results suggest that actin binding, subcellular targeting, and dimerization are associated in I/LWEQ module proteins. In this report we have used alanine-scanning mutagenesis of a putative coiled coil at the C-terminus of the Talin1 I/LWEQ module to show that the amino acids responsible for dimerization are necessary for F-actin binding, the stabilization of actin filaments, the cross-linking of actin filaments, and focal adhesion targeting. Our results suggest that this conserved dimerization motif in the I/LWEQ module plays an essential role in the function of Talin1 as a component of focal adhesions and, by extension, the other I/LWEQ module proteins in other multicomponent assemblies involved in cell adhesion and vesicle trafficking.
粘着斑复合体是与质膜相关的多组分复合体，对于整合素连接的信号转导以及细胞粘附和细胞运动至关重要。细胞骨架蛋白踝蛋白1将整合素粘附受体与肌动蛋白细胞骨架相连。踝蛋白1以及其他动物和变形虫的踝蛋白是I/LWEQ模块超家族的成员，该超家族还包括真菌的Sla2和动物的Hip1/Hip1R。I/LWEQ模块是一个保守的C端结构元件，对I/LWEQ模块蛋白的功能至关重要。踝蛋白1的I/LWEQ模块与F-肌动蛋白结合，并在体内将该蛋白靶向粘着斑。Sla2和Hip1的I/LWEQ模块是这些蛋白参与内吞作用所必需的。除了在I/LWEQ模块蛋白功能中的这些作用外，我们最近还表明I/LWEQ模块还包含一个蛋白质二聚化的决定因素。综上所述，这些结果表明肌动蛋白结合、亚细胞靶向和二聚化在I/LWEQ模块蛋白中是相关联的。在本报告中，我们对踝蛋白1的I/LWEQ模块C端的一个假定的卷曲螺旋进行了丙氨酸扫描诱变，以表明负责二聚化的氨基酸对于F-肌动蛋白结合、肌动蛋白丝的稳定、肌动蛋白丝的交联以及粘着斑靶向是必需的。我们的结果表明，I/LWEQ模块中这个保守的二聚化基序在踝蛋白1作为粘着斑组分的功能中起着至关重要的作用，并且由此延伸，在参与细胞粘附和囊泡运输的其他多组分组装体中的其他I/LWEQ模块蛋白中也起着至关重要的作用。
