Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.
Mol Biol Cell. 2012 Oct;23(19):3827-37. doi: 10.1091/mbc.E12-07-0496. Epub 2012 Aug 23.
Dynactin is an essential part of the cytoplasmic dynein motor that enhances motor processivity and serves as an adaptor that allows dynein to bind cargoes. Much is known about dynactin's interaction with dynein and microtubules, but how it associates with its diverse complement of subcellular binding partners remains mysterious. It has been suggested that cargo specification involves a group of subunits referred to as the "pointed-end complex." We used chemical cross-linking, RNA interference, and protein overexpression to characterize interactions within the pointed-end complex and explore how it contributes to dynactin's interactions with endomembranes. The Arp11 subunit, which caps one end of dynactin's Arp1 filament, and p62, which binds Arp11 and Arp1, are necessary for dynactin stability. These subunits also allow dynactin to bind the nuclear envelope prior to mitosis. p27 and p25, by contrast, are peripheral components that can be removed without any obvious impact on dynactin integrity. Dynactin lacking these subunits shows reduced membrane binding. Depletion of p27 and p25 results in impaired early and recycling endosome movement, but late endosome movement is unaffected, and mitotic spindles appear normal. We conclude that the pointed-end complex is a bipartite structural domain that stabilizes dynactin and supports its binding to different subcellular structures.
动力蛋白激活蛋白复合体是细胞质动力蛋白的一个必需组成部分，它可以增强动力蛋白的运动能力，并作为一个衔接物，使动力蛋白能够结合货物。人们对动力蛋白激活蛋白复合体与动力蛋白和微管的相互作用了解很多，但它如何与细胞内各种结合伴侣相关联仍然是个谜。有人提出，货物的特异性涉及一组被称为“尖端复合物”的亚基。我们使用化学交联、RNA 干扰和蛋白质过表达来描述尖端复合物内的相互作用，并探讨它如何促进动力蛋白与内膜的相互作用。Arp11 亚基，它覆盖动力蛋白的 Arp1 丝的一端，以及与 Arp11 和 Arp1 结合的 p62，对于动力蛋白的稳定性是必需的。这些亚基还允许动力蛋白在有丝分裂前与核膜结合。相比之下，p27 和 p25 是外围组件，去除它们不会对动力蛋白的完整性产生明显影响。缺乏这些亚基的动力蛋白显示出膜结合减少。p27 和 p25 的耗竭导致早期和再循环内体运动受损，但晚期内体运动不受影响，有丝分裂纺锤体看起来正常。我们得出结论，尖端复合物是一个二部分结构域，它稳定动力蛋白并支持其与不同的亚细胞结构结合。
