Crystal structure of human UP1, the domain of hnRNP A1 that contains two RNA-recognition motifs
Crystal structure of human UP1, the domain of hnRNP A1 that contains two RNA-recognition motifs
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DOI：
10.1016/s0969-2126(97)00211-6
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发表时间：
1997-04-15
期刊：
影响因子：
5.7
通讯作者：
Krainer, AR
中科院分区：
文献类型：
--
作者：
Xu, RM;Jokhan, L;Krainer, AR
背景：异质性核核糖核蛋白A1是后生动物核中含量最丰富的核核糖核蛋白复合体核心蛋白之一。它通过拮抗几种富含丝氨酸/精氨酸的剪接因子(SR蛋白)的活性，导致远端替代5‘剪接位点的激活和可选外显子的跳过，发挥着选择性前mRNA剪接的全球调节作用。纯化的hnRNP A1具有核酸退火活性。该蛋白质还在细胞核和细胞质之间持续穿梭，这一过程是由其C末端富含甘氨酸的区域内的信号介导的。人hnRNP A1的N末端区域被称为解卷蛋白1(UP1)，包含两个RNA识别基序(RRMS)，RRM1和RRM2。了解hnRNP A1与RNA相互作用的结构元素将对RNA加工的研究具有广泛的意义。结果：UP1的晶体结构已确定为1.9埃分辨率。每个RRM独立地采用特征的RRM折叠，由一个四链反平行的β-折叠片断和两个螺旋包装在贝塔片层的一侧。这两个RRMS是反平行的，并保持密切接触，主要由两个Arg-Asp离子对组成。结果，两个缠绕在一起的β片断被结合在一起，形成了一个延伸的RNA结合表面。连接两个RRMS的连接体的一段在没有结合RNA的情况下是灵活的，但连接体的一般位置表明它可以与RNA直接接触。与其他RRM结构的比较表明，在RRM1的第一个β链的N端立即发现一个短的3(10)螺旋，可以直接与RNA相互作用。结论：RRM是最常见和最具特征的RNA结合基序之一，在某些情况下，一个RRM就足以与序列特异性和高亲和力的RNA结合，但在其他情况下，单个蛋白质中的几个RRM之间需要协同作用。这项研究展示了两个RRMS是如何在一个多肽中组织的。UP1中的两个独立折叠的RRMS以固定的几何形式保持在一起，使两个RRMS能够作为单个实体与RNA结合，因此解释了RRMS之间的协同作用，UP1结构也表明位于RRMS外部的残基可以与RNA进行潜在的重要相互作用。
Background: Heterogeneous nuclear ribonucleoprotein (hnRNP) A1 is one of the most abundant core proteins of hnRNP complexes in metazoan nuclei. It behaves as a global regulator of alternative pre-mRNA splicing by antagonizing the activities of several serine/arginine-rich splicing factors (SR proteins), resulting in the activation of distal alternative 5' splice sites and skipping of optional exons. Purified hnRNP A1 has nucleic acid annealing activity. The protein also shuttles continuously between the nucleus and the cytoplasm, a process mediated by signals within its C-terminal glycine-rich domain. The N-terminal region of human hnRNP A1, termed unwinding protein 1 (UP1), contains two RNA-recognition motifs (RRMs), RRM1 and RRM2. Understanding the structural elements by which hnRNP A1 interacts with RNA will have broad implications for studies of RNA processing.Results: The crystal structure of UP1 has been determined to 1.9 Angstrom resolution. Each RRM independently adopts the characteristic RRM fold, consisting of a four-stranded antiparallel beta-pleated sheet and two of helices packed on one side of the beta sheet. The two RRMs are antiparallel and held in close contact, mainly by two Arg-Asp ion pairs. As a result, the two tour-stranded beta sheets are brought together to form an extended RNA-binding surface. A segment of the linker connecting the two RRMs is flexible in the absence of bound RNA, but the general location of the linker suggests that it can make direct contacts with RNA. Comparison with other RRM structures indicates that a short 3(10) helix, found immediately N-terminal to the first beta strand in RRM1, may interact with RNA directly.Conclusions: The RRM is one of the most common and best characterized RNA-binding motifs, in certain cases, one RRM is sufficient for sequence-specific and high affinity RNA binding; but in other cases, synergy between several RRMs within a single protein is required. This study shows how two RRMs are organized in a single polypeptide. The two independently folded RRMs in UP1 are held together in a fixed geometry, enabling the two RRMs to function as a single entity in binding RNA, and so explaining the synergy between the RRMs, The UP1 structure also suggests that residues which lie outside of the RRMs can make potentially important interactions with RNA.