Freie Universität Berlin, Institute of Chemistry and Biochemistry, Laboratory of Structural Biochemistry, Takustr. 6, D-14195, Berlin, Germany.
Harvard Medical School, Department of Cell Biology, 240 Longwood Avenue, Boston, MA, 02115, USA.
Nat Commun. 2023 Apr 5;14(1):1886. doi: 10.1038/s41467-023-37528-3.
Activating signal co-integrator 1 complex (ASCC) subunit 3 (ASCC3) supports diverse genome maintenance and gene expression processes, and contains tandem Ski2-like NTPase/helicase cassettes crucial for these functions. Presently, the molecular mechanisms underlying ASCC3 helicase activity and regulation remain unresolved. We present cryogenic electron microscopy, DNA-protein cross-linking/mass spectrometry as well as in vitro and cellular functional analyses of the ASCC3-TRIP4 sub-module of ASCC. Unlike the related spliceosomal SNRNP200 RNA helicase, ASCC3 can thread substrates through both helicase cassettes. TRIP4 docks on ASCC3 via a zinc finger domain and stimulates the helicase by positioning an ASC-1 homology domain next to the C-terminal helicase cassette of ASCC3, likely supporting substrate engagement and assisting the DNA exit. TRIP4 binds ASCC3 mutually exclusively with the DNA/RNA dealkylase, ALKBH3, directing ASCC3 for specific processes. Our findings define ASCC3-TRIP4 as a tunable motor module of ASCC that encompasses two cooperating NTPase/helicase units functionally expanded by TRIP4.
激活信号共整合因子 1 复合物（ASCC）亚基 3（ASCC3）支持多种基因组维护和基因表达过程，并包含串联 Ski2 样 NTPase/解旋酶盒，这些对于这些功能至关重要。目前，ASCC3 解旋酶活性和调节的分子机制仍未解决。我们提出了低温电子显微镜、DNA-蛋白质交联/质谱分析以及 ASCC 的 ASCC3-TRIP4 亚模块的体外和细胞功能分析。与相关的剪接体 SNRNP200 RNA 解旋酶不同，ASCC3 可以使底物通过两个解旋酶盒。TRIP4 通过锌指结构域与 ASCC3 对接，并通过将 ASC-1 同源结构域定位在 ASCC3 的 C 末端解旋酶盒旁边来刺激解旋酶，这可能支持底物结合并协助 DNA 出口。TRIP4 与 DNA/RNA 脱烷基酶 ALKBH3 与 ASCC3 相互排斥结合，指导 ASCC3 进行特定的过程。我们的发现将 ASCC3-TRIP4 定义为 ASCC 的可调谐马达模块，它包含两个功能扩展的协同 NTPase/解旋酶单元。
