Department of Biochemistry, Molecular Neuroscience Center, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
Proc Natl Acad Sci U S A. 2010 Mar 2;107(9):4040-5. doi: 10.1073/pnas.0911385107. Epub 2010 Feb 8.
The hereditary hearing-vision loss disease, Usher syndrome I (USH1), is caused by defects in several proteins that can interact with each other in vitro. Defects in USH1 proteins are thought to be responsible for the developmental and functional impairments of sensory cells in the retina and inner ear. Harmonin/USH1C and Sans/USH1G are two of the USH1 proteins that interact with each other. Harmonin also binds to other USH1 proteins such as cadherin 23 (CDH23) and protocadherin 15 (PCDH15). However, the molecular basis governing the harmonin and Sans interaction is largely unknown. Here, we report an unexpected assembly mode between harmonin and Sans. We demonstrate that the N-terminal domain and the first PDZ domain of harmonin are tethered by a small-domain C-terminal to PDZ1 to form a structural and functional supramodule responsible for binding to Sans. We discover that the SAM domain of Sans, specifically, binds to the PDZ domain of harmonin, revealing previously unknown interaction modes for both PDZ and SAM domains. We further show that the synergistic PDZ1/SAM and PDZ1/carboxyl PDZ binding-motif interactions, between harmonin and Sans, lock the two scaffold proteins into a highly stable complex. Mutations in harmonin and Sans found in USH1 patients are shown to destabilize the complex formation of the two proteins.
遗传性听力视力丧失疾病，Usher 综合征 I（USH1），是由几种可以在体外相互作用的蛋白质缺陷引起的。人们认为 USH1 蛋白的缺陷是导致视网膜和内耳感觉细胞发育和功能障碍的原因。Harmonin/USH1C 和 Sans/USH1G 是相互作用的两种 USH1 蛋白之一。Harmonin 还与其他 USH1 蛋白（如钙粘蛋白 23（CDH23）和原钙粘蛋白 15（PCDH15））相互作用。然而，控制 harmonin 和 Sans 相互作用的分子基础在很大程度上是未知的。在这里，我们报告了 harmonin 和 Sans 之间一种出乎意料的组装模式。我们证明，harmonin 的 N 端结构域和第一 PDZ 结构域通过一个小的 C 端结构域与 PDZ1 连接，形成一个负责与 Sans 结合的结构和功能超模块。我们发现，Sans 的 SAM 结构域特异性地与 harmonin 的 PDZ 结构域结合，揭示了 PDZ 和 SAM 结构域以前未知的相互作用模式。我们进一步表明，harmonin 和 Sans 之间的协同 PDZ1/SAM 和 PDZ1/羧基 PDZ 结合基序相互作用将这两种支架蛋白锁定在一个高度稳定的复合物中。在 USH1 患者中发现的 harmonin 和 Sans 突变会破坏这两种蛋白质的复合物形成。
