Webb A E, Weeks K M
Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, USA.
Nat Struct Biol. 2001 Feb;8(2):135-40. doi: 10.1038/84124.
Most large RNAs achieve their active, native structures only as complexes with one or more cofactor proteins. By varying the Mg(2+) concentration, the catalytic core of the bI5 group I intron RNA can be manipulated into one of three states, expanded, collapsed or native, or into balanced equilibria between these states. Under near-physiological conditions, the bI5 RNA folds rapidly to a collapsed but non-native state. Hydroxyl radical footprinting demonstrates that assembly with the CBP2 protein cofactor chases the RNA from the collapsed state to the native state. In contrast, CBP2 also binds to the RNA in the expanded state to form many non-native interactions. This structural picture is reinforced by functional splicing experiments showing that RNA in an expanded state forms a non-productive, kinetically trapped complex with CBP2. Thus, rapid folding to the collapsed state functions to self-chaperone bI5 RNA folding by preventing premature interaction with its protein cofactor. This productive, self-chaperoning role for RNA collapsed states may be especially important to avert misassembly of large multi-component RNA-protein machines in the cell.
大多数大型RNA只有与一种或多种辅助蛋白形成复合物才能形成其活性天然结构。通过改变Mg(2+)浓度，I组内含子bI5 RNA的催化核心可被调控为三种状态之一：扩展态、折叠态或天然态，或这些状态之间的平衡态。在接近生理条件下，bI5 RNA迅速折叠成折叠但非天然的状态。羟基自由基足迹法表明，与CBP2蛋白辅助因子组装可使RNA从折叠态转变为天然态。相反，CBP2也会与扩展态的RNA结合，形成许多非天然相互作用。功能性剪接实验进一步证实了这一结构情况，实验表明处于扩展态的RNA与CBP2形成了非生产性的、动力学上被困住的复合物。因此，快速折叠成折叠态通过防止与蛋白辅助因子过早相互作用，起到了自我陪伴bI5 RNA折叠的作用。RNA折叠态的这种有效自我陪伴作用对于避免细胞中大型多组分RNA-蛋白质机器的错误组装可能尤为重要。
