Ecole Polytechnique Fédérale de Lausanne (EPFL), School of Life Sciences, SV ISREC, Station 19, 1015 Lausanne, Switzerland.
Department of Chemistry and Biochemistry, UCLA-DOE Institute of Genomics and Proteomics, Molecular Biology Institute, University of California, Los Angeles, Boyer Hall, 611 Charles E. Young Drive East, Los Angeles, CA 90095-1570, USA.
Structure. 2018 Feb 6;26(2):209-224.e6. doi: 10.1016/j.str.2017.12.002. Epub 2017 Dec 28.
Head-to-tail polymers of sterile alpha motifs (SAM) can scaffold large macromolecular complexes. Several SAM-domain proteins that bind each other are mutated in patients with cystic kidneys or laterality defects, including the Ankyrin (ANK) and SAM domain-containing proteins ANKS6 and ANKS3, and the RNA-binding protein Bicc1. To address how their interactions are regulated, we first determined a high-resolution crystal structure of a Bicc1-SAM polymer, revealing a canonical SAM polymer with a high degree of flexibility in the subunit interface orientations. We further mapped interactions between full-length and distinct domains of Bicc1, ANKS3, and ANKS6. Neither ANKS3 nor ANKS6 alone formed macroscopic homopolymers in vivo. However, ANKS3 recruited ANKS6 to Bicc1, and the three proteins together cooperatively generated giant macromolecular complexes. Thus, the giant assemblies are shaped by SAM domains, their flanking sequences, and SAM-independent protein-protein and protein-mRNA interactions.
无菌α基序（SAM）的头到尾聚合物可以支架大分子复合物。在囊性肾脏或侧位缺陷的患者中，几种相互结合的 SAM 结构域蛋白发生突变，包括锚蛋白（ANK）和含有 SAM 结构域的蛋白 ANKS6 和 ANKS3，以及 RNA 结合蛋白 Bicc1。为了解决它们的相互作用如何被调节，我们首先确定了 Bicc1-SAM 聚合物的高分辨率晶体结构，揭示了具有高度灵活性的经典 SAM 聚合物在亚基界面取向。我们进一步绘制了全长和 Bicc1、ANKS3 和 ANKS6 不同结构域之间的相互作用。ANKS3 和 ANKS6 单独都不能在体内形成宏观同聚物。然而，ANKS3 将 ANKS6 招募到 Bicc1，这三种蛋白质一起协同生成巨型大分子复合物。因此，巨组装由 SAM 结构域、其侧翼序列以及 SAM 独立的蛋白质-蛋白质和蛋白质-RNA 相互作用形成。
