Wei Zhiyi, Li Youjun, Ye Fei, Zhang Mingjie
From the Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China, Center of Systems Biology and Human Health, School of Science and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China, and Department of Biology, South University of Science and Technology of China, Shenzhen 518055, China.
From the Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
J Biol Chem. 2015 May 1;290(18):11384-92. doi: 10.1074/jbc.M115.643791. Epub 2015 Mar 19.
The type I transmembrane protein crumbs (Crb) plays critical roles in the establishment and maintenance of cell polarities in diverse tissues. As such, mutations of Crb can cause different forms of cancers. The cell intrinsic role of Crb in cell polarity is governed by its conserved, 37-residue cytoplasmic tail (Crb-CT) via binding to moesin and protein associated with Lin7-1 (PALS1). However, the detailed mechanism governing the Crb·moesin interaction and the balance of Crb in binding to moesin and PALS1 are not well understood. Here we report the 1.5 Å resolution crystal structure of the moesin protein 4.1/ezrin/radixin/moesin (FERM)·Crb-CT complex, revealing that both the canonical FERM binding motif and the postsynaptic density protein-95/Disc large-1/Zonula occludens-1 (PDZ) binding motif of Crb contribute to the Crb·moesin interaction. We further demonstrate that phosphorylation of Crb-CT by atypical protein kinase C (aPKC) disrupts the Crb·moesin association but has no impact on the Crb·PALS1 interaction. The above results indicate that, upon the establishment of the apical-basal polarity in epithelia, apical-localized aPKC can actively prevent the Crb·moesin complex formation and thereby shift Crb to form complex with PALS1 at apical junctions. Therefore, Crb may serve as an aPKC-mediated sensor in coordinating contact-dependent cell growth inhibition in epithelial tissues.
I型跨膜蛋白crumbs（Crb）在多种组织细胞极性的建立和维持中发挥关键作用。因此，Crb突变可导致不同形式的癌症。Crb在细胞极性中的细胞内在作用由其保守的37个氨基酸的细胞质尾巴（Crb-CT）通过与埃兹蛋白（moesin）和与Lin7-1相关的蛋白（PALS1）结合来调控。然而，调控Crb与埃兹蛋白相互作用以及Crb与埃兹蛋白和PALS1结合平衡的详细机制尚不清楚。在此，我们报道了埃兹蛋白的4.1/埃兹蛋白/根蛋白/埃兹蛋白（FERM）·Crb-CT复合物的1.5 Å分辨率晶体结构，揭示了Crb的经典FERM结合基序和突触后致密蛋白95/盘状大蛋白1/紧密连接蛋白1（PDZ）结合基序均有助于Crb与埃兹蛋白的相互作用。我们进一步证明，非典型蛋白激酶C（aPKC）对Crb-CT的磷酸化破坏了Crb与埃兹蛋白的结合，但对Crb与PALS1的相互作用没有影响。上述结果表明，在上皮细胞顶-基极性建立后，位于顶端的aPKC可主动阻止Crb与埃兹蛋白复合物的形成，从而促使Crb在上皮细胞顶端连接处与PALS1形成复合物。因此，Crb可能作为一种aPKC介导的传感器，在上皮组织中协调接触依赖性细胞生长抑制。
