Structural Motility, Institut Curie, PSL Research University, CNRS, UMR 144, F-75005 Paris, France.
Sorbonne Universités, UPMC Univ Paris 06, Sorbonne Universités, IFD, 4 Place Jussieu 75252 Paris, France.
Nat Commun. 2017 Jun 29;8:15864. doi: 10.1038/ncomms15864.
Cadherin linkages between adjacent stereocilia and microvilli are essential for mechanotransduction and maintaining their organization. They are anchored to actin through interaction of their cytoplasmic domains with related tripartite complexes consisting of a class VII myosin and adaptor proteins: Myo7a/SANS/Harmonin in stereocilia and Myo7b/ANKS4B/Harmonin in microvilli. Here, we determine high-resolution structures of Myo7a and Myo7b C-terminal MyTH4-FERM domain (MF2) and unveil how they recognize harmonin using a novel binding mode. Systematic definition of interactions between domains of the tripartite complex elucidates how the complex assembles and prevents possible self-association of harmonin-a. Several Myo7a deafness mutants that map to the surface of MF2 disrupt harmonin binding, revealing the molecular basis for how they impact the formation of the tripartite complex and disrupt mechanotransduction. Our results also suggest how switching between different harmonin isoforms can regulate the formation of networks with Myo7a motors and coordinate force sensing in stereocilia.
细胞黏附分子连接相邻的静纤毛和微绒毛对于机械转导和维持它们的结构至关重要。它们通过细胞内结构域与相关的三部分复合物相互作用锚定在肌动蛋白上，该复合物由 VII 类肌球蛋白和衔接蛋白组成：静纤毛中的 Myo7a/SANS/Harmonin 和微绒毛中的 Myo7b/ANKS4B/Harmonin。在这里，我们确定了 Myo7a 和 Myo7b C 端 MyTH4-FERM 结构域 (MF2) 的高分辨率结构，并揭示了它们如何使用新的结合模式识别 harmonin。对三部分复合物各结构域之间相互作用的系统定义阐明了复合物是如何组装的，以及如何防止 harmonin-a 的可能自聚集。几个映射到 MF2 表面的 Myo7a 耳聋突变体破坏了 harmonin 的结合，揭示了它们如何影响三部分复合物的形成并破坏机械转导的分子基础。我们的结果还表明，不同 harmonin 同工型之间的转换如何调节与 Myo7a 马达形成的网络以及协调静纤毛中的力感应。
