Aderounmu Adedeji M, Maus-Conn Josephine, Consalvo Claudia D, Shen Peter S, Bass Brenda L
Department of Biochemistry, University of Utah, Salt Lake City, UT 84112.
Proc Natl Acad Sci U S A. 2025 Jun 3;122(22):e2500825122. doi: 10.1073/pnas.2500825122. Epub 2025 May 28.
A fully functional Dicer helicase, present in the modern arthropod, uses energy from ATP hydrolysis to power translocation on bound dsRNA, enabling the processive dsRNA cleavage required for efficient antiviral defense. However, modern Dicer orthologs exhibit divergent helicase functions that affect their ability to contribute to antiviral defense. Moreover, mechanisms that couple ATP hydrolysis to Dicer helicase movement on dsRNA remain enigmatic. We used biochemical and structural analyses of ancestrally reconstructed Dicer helicases to map evolution of dsRNA binding affinity, ATP hydrolysis and translocation. Loss of affinity for dsRNA occurred early in Dicer evolution, coinciding with a decline in translocation activity, despite preservation of ATP hydrolysis activity. Ancestral nematode Dicer also exhibited significant decline in ATP hydrolysis and translocation, but studies of antiviral activities in the modern nematode indicate Dicer retained a role in antiviral defense by recruiting a second helicase. Cryogenic electron microscopy (cryo-EM) analyses of an ancient metazoan Dicer allowed capture of multiple helicase states revealing the mechanism that connects each step of ATP hydrolysis to unidirectional movement along dsRNA. Our study rationalizes the diversity in modern Dicer helicases by connecting ancestral functions to observations in extant enzymes.
现代节肢动物中存在一种功能完备的Dicer解旋酶，它利用ATP水解产生的能量为其在结合的双链RNA上的易位提供动力，从而实现高效抗病毒防御所需的持续性双链RNA切割。然而，现代Dicer直系同源物表现出不同的解旋酶功能，这影响了它们对抗病毒防御的贡献能力。此外，将ATP水解与Dicer解旋酶在双链RNA上的移动相耦合的机制仍然是个谜。我们利用对祖先重建的Dicer解旋酶的生化和结构分析，来绘制双链RNA结合亲和力、ATP水解和易位的进化图谱。在Dicer进化早期就出现了对双链RNA亲和力的丧失，这与易位活性的下降同时发生，尽管ATP水解活性得以保留。线虫祖先的Dicer在ATP水解和易位方面也表现出显著下降，但对现代线虫抗病毒活性的研究表明，Dicer通过招募另一种解旋酶在抗病毒防御中保留了作用。对一种古老后生动物Dicer的低温电子显微镜（cryo-EM）分析，捕捉到了多种解旋酶状态，揭示了将ATP水解的每一步与沿双链RNA的单向移动相联系的机制。我们的研究通过将祖先功能与现存酶的观察结果联系起来，解释了现代Dicer解旋酶的多样性。
