Department of Biochemistry and Biophysics, School of Medicine, The University of North Carolina, Chapel Hill, Chapel Hill, NC 27599, USA.
Division of Chemical Biology and Medicinal Chemistry, Eshelman School of Pharmacy, The University of North Carolina, Chapel Hill, Chapel Hill, NC 27599, USA.
Cell Rep. 2019 Feb 12;26(7):1681-1690.e5. doi: 10.1016/j.celrep.2019.01.058.
Histone H3 lysine 79 (H3K79) methylation is enriched on actively transcribed genes, and its misregulation is a hallmark of leukemia. Methylation of H3K79, which resides on the structured disk face of the nucleosome, is mediated by the Dot1L methyltransferase. Dot1L activity is part of a trans-histone crosstalk pathway, requiring prior histone H2B ubiquitylation of lysine 120 (H2BK120ub) for optimal activity. However, the molecular details describing both how Dot1L binds to the nucleosome and why Dot1L is activated by H2BK120 ubiquitylation are unknown. Here, we present the cryoelectron microscopy (cryo-EM) structure of Dot1L bound to a nucleosome reconstituted with site-specifically ubiquitylated H2BK120. The structure reveals that Dot1L engages the nucleosome acidic patch using a variant arginine anchor and occupies a conformation poised for methylation. In this conformation, Dot1L and ubiquitin interact directly through complementary hydrophobic surfaces. This study establishes a path to better understand Dot1L function in normal and leukemia cells.
组蛋白 H3 赖氨酸 79（H3K79）甲基化富集在活跃转录的基因上，其调控失调是白血病的一个标志。H3K79 上的甲基化位于核小体的结构化盘面上，由 Dot1L 甲基转移酶介导。Dot1L 活性是跨组蛋白相互作用途径的一部分，需要先前的组蛋白 H2B 赖氨酸 120（H2BK120ub）泛素化，以实现最佳活性。然而，描述 Dot1L 如何结合核小体以及为什么 Dot1L 被 H2BK120 泛素化激活的分子细节尚不清楚。在这里，我们展示了与通过定点泛素化 H2BK120 重建的核小体结合的 Dot1L 的冷冻电子显微镜（cryo-EM）结构。该结构表明，Dot1L 使用变体精氨酸锚定点与核小体的酸性斑结合，并占据了甲基化的构象。在这种构象中，Dot1L 和泛素通过互补的疏水面直接相互作用。这项研究为更好地理解 Dot1L 在正常和白血病细胞中的功能奠定了基础。
