McMillan Brian J, Tibbe Christine, Drabek Andrew A, Seegar Tom C M, Blacklow Stephen C, Klein Thomas
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
Institute of Genetics, Heinrich-Heine-University, Dusseldorf 40225, Germany.
Cell Rep. 2017 May 30;19(9):1750-1757. doi: 10.1016/j.celrep.2017.05.026.
The ESCRT-III complex induces outward membrane budding and fission through homotypic polymerization of its core component Shrub/CHMP4B. Shrub activity is regulated by its direct interaction with a protein called Lgd in flies, or CC2D1A or B in humans. Here, we report the structural basis for this interaction and propose a mechanism for regulation of polymer assembly. The isolated third DM14 repeat of Lgd binds Shrub, and an Lgd fragment containing only this DM14 repeat and its C-terminal C2 domain is sufficient for in vivo function. The DM14 domain forms a helical hairpin with a conserved, positively charged tip, that, in the structure of a DM14 domain-Shrub complex, occupies a negatively charged surface of Shrub that is otherwise used for homopolymerization. Lgd mutations at this interface disrupt its function in flies, confirming functional importance. Together, these data argue that Lgd regulates ESCRT activity by controlling access to the Shrub self-assembly surface.
ESCRT-III复合物通过其核心组分Shrub/CHMP4B的同型聚合诱导向外的膜出芽和裂变。Shrub的活性受其与果蝇中一种名为Lgd的蛋白质或人类中的CC2D1A或B的直接相互作用调节。在这里，我们报道了这种相互作用的结构基础，并提出了聚合物组装调控机制。分离出的Lgd的第三个DM14重复序列与Shrub结合，并且仅包含该DM14重复序列及其C端C2结构域的Lgd片段在体内功能上就足够了。DM14结构域形成一个带有保守的带正电荷末端的螺旋发夹结构，在DM14结构域-Shrub复合物的结构中，该末端占据Shrub的一个带负电荷的表面，否则该表面用于同聚作用。该界面处的Lgd突变破坏其在果蝇中的功能，证实了功能重要性。总之，这些数据表明Lgd通过控制对Shrub自组装表面通道来调节ESCRT活性。
