Del Campo Mark, Lambowitz Alan M
Institute for Cellular and Molecular Biology, University of Texas at Austin, 78712, USA.
Mol Cell. 2009 Sep 11;35(5):598-609. doi: 10.1016/j.molcel.2009.07.032.
The yeast DEAD box protein Mss116p is a general RNA chaperone that functions in mitochondrial group I and II intron splicing, translational activation, and RNA end processing. Here we determined high-resolution X-ray crystal structures of Mss116p complexed with an RNA oligonucleotide and ATP analogs AMP-PNP, ADP-BeF(3)(-), or ADP-AlF(4)(-). The structures show the entire helicase core acting together with a functionally important C-terminal extension. In all structures, the helicase core is in a closed conformation with a wedge alpha helix bending RNA 3' of the central bound nucleotides, as in previous DEAD box protein structures. Notably, Mss116p's C-terminal extension also bends RNA 5' of the central nucleotides, resulting in RNA crimping. Despite reported functional differences, we observe few structural changes in ternary complexes with different ATP analogs. The structures constrain models of DEAD box protein function and reveal a strand separation mechanism in which a protein uses two wedges to act as a molecular crimper.
酵母DEAD盒蛋白Mss116p是一种通用的RNA伴侣，在线粒体I类和II类内含子剪接、翻译激活及RNA末端加工过程中发挥作用。在此，我们确定了Mss116p与RNA寡核苷酸及ATP类似物AMP-PNP、ADP-BeF3(-)或ADP-AlF4(-)复合的高分辨率X射线晶体结构。这些结构显示整个解旋酶核心与一个具有功能重要性的C末端延伸区协同作用。在所有结构中，解旋酶核心处于封闭构象，其中一个楔形α螺旋使中心结合核苷酸3'端的RNA发生弯曲，如同先前的DEAD盒蛋白结构。值得注意的是，Mss116p的C末端延伸区还使中心核苷酸5'端的RNA发生弯曲，导致RNA卷曲。尽管报道了功能差异，但我们观察到与不同ATP类似物形成的三元复合物中几乎没有结构变化。这些结构限制了DEAD盒蛋白功能模型，并揭示了一种链分离机制，即一种蛋白质利用两个楔形结构充当分子卷曲钳。
