Mechanobiology Institute, National University of Singapore, Singapore.
Biophys J. 2011 Sep 7;101(5):1231-7. doi: 10.1016/j.bpj.2011.07.028.
Prompted by recent reports suggesting that interaction of filamin A (FLNa) with its binding partners is regulated by mechanical force, we examined mechanical properties of FLNa domains using magnetic tweezers. FLNa, an actin cross-linking protein, consists of two subunits that dimerize through a C-terminal self-association domain. Each subunit contains an N-terminal spectrin-related actin-binding domain followed by 24 immunoglobulinlike (Ig) repeats. The Ig repeats in the rod 1 segment (repeats 1-15) are arranged as a linear array, whereas rod 2 (repeats 16-23) is more compact due to interdomain interactions. In the rod 1 segment, repeats 9-15 augment F-actin binding to a much greater extent than do repeats 1-8. Here, we report that the three segments are unfolded at different forces under the same loading rate. Remarkably, we found that repeats 16-23 are susceptible to forces of ∼10 pN or even less, whereas the repeats in the rod 1 segment can withstand significantly higher forces. The differential force response of FLNa Ig domains has broad implications, since these domains not only support the tension of actin network but also interact with many transmembrane and signaling proteins, mostly in the rod 2 segment. In particular, our finding of unfolding of repeats 16-23 at ∼10 pN or less is consistent with the hypothesized force-sensing function of the rod 2 segment in FLNa.
受最近有报道称细丝蛋白 A（FLNa）与其结合伴侣的相互作用受机械力调控的启发，我们使用磁镊研究了 FLNa 结构域的力学性质。FLNa 是一种肌动蛋白交联蛋白，由两个通过 C 端自缔合结构域二聚化的亚基组成。每个亚基包含一个 N 端血影蛋白相关肌动蛋白结合结构域，其后是 24 个免疫球蛋白样（Ig）重复序列。杆 1 段（重复 1-15）的 Ig 重复序列排列成线性阵列，而由于结构域之间的相互作用，杆 2（重复 16-23）更加紧凑。在杆 1 段中，重复序列 9-15 比重复序列 1-8 更能显著增强肌动蛋白的结合。在此，我们报告在相同的加载速率下，三个结构域在不同的力下展开。值得注意的是，我们发现重复序列 16-23 在约 10 pN 或更小的力下容易展开，而杆 1 段中的重复序列可以承受更高的力。FLNa Ig 结构域的这种力响应差异具有广泛的意义，因为这些结构域不仅支撑肌动蛋白网络的张力，而且与许多跨膜和信号蛋白相互作用，主要发生在杆 2 段。特别是，我们发现重复序列 16-23 在约 10 pN 或更小的力下展开，这与假设的 FLNa 中杆 2 段的力传感功能一致。
