Pentikäinen Ulla, Ylänne Jari
Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland.
J Mol Biol. 2009 Oct 30;393(3):644-57. doi: 10.1016/j.jmb.2009.08.035. Epub 2009 Aug 20.
The ability of adhesion receptors to transmit biochemical signals and mechanical force across cell membranes depends on interactions with the actin cytoskeleton. Human filamins are large actin cross-linking proteins that connect integrins to the cytoskeleton. Filamin binding to the cytoplasmic tail of beta integrins has been shown to prevent integrin activation in cells, which is important for controlling cell adhesion and migration. The molecular-level mechanism for filamin binding to integrin has been unclear, however, as it was recently demonstrated that filamin undergoes intramolecular auto-inhibition of integrin binding. In this study, using steered molecular dynamics simulations, we found that mechanical force applied to filamin can expose cryptic integrin binding sites. The forces required for this are considerably lower than those for filamin immunoglobulin domain unfolding. The mechanical-force-induced unfolding of filamin and exposure of integrin binding sites occur through stable intermediates where integrin binding is possible. Accordingly, our results support filamin's role as a mechanotransducer, since force-induced conformational changes allow binding of integrin and other transmembrane and intracellular proteins. This observed force-induced conformational change can also be one of possible mechanisms involved in the regulation of integrin activation.
黏附受体跨细胞膜传递生化信号和机械力的能力取决于其与肌动蛋白细胞骨架的相互作用。人细丝蛋白是一种大型肌动蛋白交联蛋白，可将整合素连接到细胞骨架。细丝蛋白与β整合素细胞质尾部的结合已被证明可防止细胞中整合素的激活，这对于控制细胞黏附和迁移很重要。然而，细丝蛋白与整合素结合的分子水平机制尚不清楚，因为最近有研究表明细丝蛋白会发生整合素结合的分子内自抑制。在本研究中，我们使用定向分子动力学模拟发现，施加在细丝蛋白上的机械力可暴露隐蔽的整合素结合位点。实现这一点所需的力远低于细丝蛋白免疫球蛋白结构域展开所需的力。细丝蛋白的机械力诱导展开和整合素结合位点的暴露通过整合素可能结合的稳定中间体发生。因此，我们的结果支持细丝蛋白作为机械转导分子的作用，因为力诱导的构象变化允许整合素与其他跨膜和细胞内蛋白结合。这种观察到的力诱导构象变化也可能是参与整合素激活调节的可能机制之一。
