State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou 510060, China.
Department of Oncology, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China.
Nucleic Acids Res. 2020 Mar 18;48(5):2733-2748. doi: 10.1093/nar/gkaa049.
Family with sequence similarity (FAM46) proteins are newly identified metazoan-specific poly(A) polymerases (PAPs). Although predicted as Gld-2-like eukaryotic non-canonical PAPs, the detailed architecture of FAM46 proteins is still unclear. Exact biological functions for most of FAM46 proteins also remain largely unknown. Here, we report the first crystal structure of a FAM46 protein, FAM46B. FAM46B is composed of a prominently larger N-terminal catalytic domain as compared to known eukaryotic PAPs, and a C-terminal helical domain. FAM46B resembles prokaryotic PAP/CCA-adding enzymes in overall folding as well as certain inter-domain connections, which distinguishes FAM46B from other eukaryotic non-canonical PAPs. Biochemical analysis reveals that FAM46B is an active PAP, and prefers adenosine-rich substrate RNAs. FAM46B is uniquely and highly expressed in human pre-implantation embryos and pluripotent stem cells, but sharply down-regulated following differentiation. FAM46B is localized to both cell nucleus and cytosol, and is indispensable for the viability of human embryonic stem cells. Knock-out of FAM46B is lethal. Knock-down of FAM46B induces apoptosis and restricts protein synthesis. The identification of the bacterial-like FAM46B, as a pluripotent stem cell-specific PAP involved in the maintenance of translational efficiency, provides important clues for further functional studies of this PAP in the early embryonic development of high eukaryotes.
家族与序列相似性 (FAM46) 蛋白是新鉴定的后生动物特异性多聚 (A) 聚合酶 (PAP)。尽管被预测为 Gld-2 样真核非典型 PAP，但 FAM46 蛋白的详细结构仍不清楚。大多数 FAM46 蛋白的确切生物学功能也知之甚少。在这里，我们报告了第一个 FAM46 蛋白，FAM46B 的晶体结构。FAM46B 由一个明显较大的 N 端催化结构域和 C 端螺旋结构域组成，与已知的真核 PAP 相比。FAM46B 在整体折叠以及某些结构域之间的连接上与原核 PAP/CCA-添加酶相似，这使其与其他真核非典型 PAP 区分开来。生化分析表明 FAM46B 是一种活性 PAP，并且优先选择富含腺苷的底物 RNA。FAM46B 在人类植入前胚胎和多能干细胞中特异性且高度表达，但在分化后急剧下调。FAM46B 定位于细胞核和细胞质，对人类胚胎干细胞的活力是不可或缺的。FAM46B 的敲除是致命的。FAM46B 的敲低会诱导细胞凋亡并限制蛋白质合成。具有细菌样特征的 FAM46B 作为一种参与维持翻译效率的多能干细胞特异性 PAP 的鉴定，为进一步研究该 PAP 在高等真核生物早期胚胎发育中的功能提供了重要线索。
