Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA; Stanford Cancer Institute, Stanford University School of Medicine, Stanford, CA 94305, USA.
Center for Personal Dynamic Regulomes and Program in Epithelial Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Cell. 2018 Jun 28;174(1):218-230.e13. doi: 10.1016/j.cell.2018.04.039. Epub 2018 May 24.
Ribonucleoprotein enzymes require dynamic conformations of their RNA constituents for regulated catalysis. Human telomerase employs a non-coding RNA (hTR) with a bipartite arrangement of domains-a template-containing core and a distal three-way junction (CR4/5) that stimulates catalysis through unknown means. Here, we show that telomerase activity unexpectedly depends upon the holoenzyme protein TCAB1, which in turn controls conformation of CR4/5. Cells lacking TCAB1 exhibit a marked reduction in telomerase catalysis without affecting enzyme assembly. Instead, TCAB1 inactivation causes unfolding of CR4/5 helices that are required for catalysis and for association with the telomerase reverse-transcriptase (TERT). CR4/5 mutations derived from patients with telomere biology disorders provoke defects in catalysis and TERT binding similar to TCAB1 inactivation. These findings reveal a conformational "activity switch" in human telomerase RNA controlling catalysis and TERT engagement. The identification of two discrete catalytic states for telomerase suggests an intramolecular means for controlling telomerase in cancers and progenitor cells.
核糖核蛋白酶需要其 RNA 成分的动态构象来进行调节催化。人类端粒酶采用一种非编码 RNA（hTR），其结构域分为两部分——包含模板的核心和远端三链连接（CR4/5），通过未知的方式刺激催化。在这里，我们表明端粒酶活性出乎意料地依赖于全酶蛋白 TCAB1，而 TCAB1 又控制着 CR4/5 的构象。缺乏 TCAB1 的细胞表现出端粒酶催化作用明显减少，而不影响酶的组装。相反，TCAB1 的失活导致催化所需的 CR4/5 螺旋的展开，以及与端粒酶逆转录酶（TERT）的结合。源自端粒生物学紊乱患者的 CR4/5 突变引起催化和 TERT 结合缺陷，类似于 TCAB1 的失活。这些发现揭示了人类端粒酶 RNA 控制催化和 TERT 结合的构象“活性开关”。端粒酶两种离散催化状态的鉴定为控制癌症和祖细胞中端粒酶提供了一种分子内手段。
