DEAD-box helicases (DDXs) regulate RNA processing and metabolism by unwinding short double-stranded (ds) RNAs. Sharing a helicase core composed of two RecA-like domains (D1D2), DDXs function in an ATP-dependent, non-processive manner. As an attractive target for cancer and AIDS treatment, DDX3X and its orthologs are extensively studied, yielding a wealth of biochemical and biophysical data, including structures of apo-D1D2 and post-unwound D1D2:single-stranded RNA complex, and the structure of a D2:dsRNA complex that is thought to represent a pre-unwound state. However, the structure of a pre-unwound D1D2:dsRNA complex remains elusive, and thus, the mechanism of DDX action is not fully understood. Here, we describe the structure of a D1D2 core in complex with a 23-base pair dsRNA at pre-unwound state, revealing that two DDXs recognize a 2-turn dsRNA, each DDX mainly recognizes a single RNA strand, and conformational changes induced by ATP binding unwinds the RNA duplex in a cooperative manner.

DEAD-box解旋酶（DDXs）通过展开短的双链（ds）RNA来调节RNA的加工和代谢。DDX共享由两个类似RecA的域（D1D2）组成的解旋酶核心，以ATP依赖的非过程方式起作用。作为治疗癌症和艾滋病的诱人靶标，对DDX3X及其直系同源物进行了广泛的研究，产生了丰富的生化和生物物理数据，包括载脂蛋白D1D2和解绕后的D1D2：单链RNA复合物，以及apo-D1D2的结构。 D2：dsRNA复合物，被认为代表解开前的状态。但是，解绕前的D1D2：dsRNA复合物的结构仍然难以捉摸，因此，对DDX作用的机制还没有完全了解。在这里，我们描述了在解链前与23个碱基对的dsRNA复合的D1D2核心的结构，