Department of Cellular Physiology and Metabolism, University Medical Center, University of Geneva, 1211 Geneva 4, Switzerland.
J Cell Biol. 2009 Nov 30;187(5):715-31. doi: 10.1083/jcb.200908134. Epub 2009 Nov 23.
Integrin-dependent adhesion sites consist of clustered integrins that transmit mechanical forces and provide signaling required for cell survival and morphogenesis. Despite their importance, the regulation of integrin clustering by the cytoplasmic adapter protein talin (Tal) and phosphatidylinositol (PI)-4,5-biphosphate (PI(4,5)P(2)) lipids nor their dynamic coupling to the actin cytoskeleton is fully understood. By using a Tal-dependent integrin clustering assay in intact cells, we identified a PI(4,5)P(2)-binding basic ridge spanning across the F2 and F3 domains of the Tal head that regulates integrin clustering. Clustering requires a new PI(4,5)P(2)-binding site in F2 and is negatively regulated by autoinhibitory interactions between F3 and the Tal rod (Tal-R). The release of the Tal-R exposes a new beta3-integrin-binding site in F3, enabling interaction with a membrane proximal acidic motif, which involves the formation of salt bridges between K(316) and K(324) with E(726) and D(723), respectively. This interaction shields the beta-integrin tail from reassociation with its alpha subunit, thereby maintaining the integrin in a substrate-binding and clustering-competent form.
整合素依赖的黏附位点由聚集的整合素组成,这些整合素传递机械力,并提供细胞存活和形态发生所需的信号。尽管它们很重要,但细胞质衔接蛋白 talin(Tal)和磷脂酰肌醇(PI)-4,5-二磷酸(PI(4,5)P(2))脂质对整合素聚集的调节及其与肌动蛋白细胞骨架的动态偶联都尚未完全了解。通过在完整细胞中使用依赖 Tal 的整合素聚集测定法,我们鉴定出横跨 Tal 头部的 F2 和 F3 结构域的一个 PI(4,5)P(2)结合碱性脊,该脊调节整合素的聚集。聚集需要 F2 中一个新的 PI(4,5)P(2)结合位点,并且被 F3 与 Tal 杆(Tal-R)之间的自动抑制相互作用负调节。Tal-R 的释放暴露出 F3 中一个新的β3 整合素结合位点,使其能够与膜近端酸性基序相互作用,这涉及到 K(316)和 K(324)与 E(726)和 D(723)之间形成盐桥。这种相互作用使β整合素尾部与它的α亚基重新结合,从而使整合素保持在底物结合和聚集能力的形式。