Structure of the archaeal Cascade subunit Csa5: relating the small subunits of CRISPR effector complexes.
Structure of the archaeal Cascade subunit Csa5: relating the small subunits of CRISPR effector complexes.
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DOI：
10.4161/rna.23854
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发表时间：
2013-05
期刊：
影响因子：
4.1
通讯作者：
Naismith JH
中科院分区：
文献类型：
--
作者：
Reeks J;Graham S;Anderson L;Liu H;White MF;Naismith JH
用于CRISPR介导的抗病毒免疫的Cascade复合体使用CRISPR RNA （crRNA）靶向来自移动元件（如病毒）的入侵DNA物种，导致它们被破坏。级联效应复合物的核心由Cas5和Cas7亚基组成，它们在原核生物中广泛保守。Cas7结合crRNA，形成Cascade的螺旋骨架。许多古细菌编码一种Cascade复合体（标记为I-A型），其中包括Csa5（或小）亚基，它与核心蛋白相互作用弱。在这里，我们报道了来自solfataricus的Csa5蛋白的晶体结构。Csa5包含一个保守的α-螺旋结构域和一个由弱保守的β-链结构域组成的小插入。在晶体中，Csa5单体聚合成无限螺旋线。在每个界面上都有一个严格保守的亚基间盐桥，它的缺失会破坏多聚。结构分析表明，CRISPR效应复合物的小亚基之间具有共同的进化史。同样的α-螺旋结构域存在于Cse2的c端结构域（来自Type I-E Cascade），而Cse2的n端结构域存在于CMR （Type III-B）效应复合物的Cmr5中。由于Cmr5与Csa5不匹配，存在两种可能性：从祖先的Cse2中选择性地丢失域以产生两个新的亚家族或两个独立家族的域融合以产生新的Cse2家族。一个明确的答案有待于对其他CRISPR效应复合物的进一步小亚基的结构研究。
The Cascade complex for CRISPR-mediated antiviral immunity uses CRISPR RNA (crRNA) to target invading DNA species from mobile elements such as viruses, leading to their destruction. The core of the Cascade effector complex consists of the Cas5 and Cas7 subunits, which are widely conserved in prokaryotes. Cas7 binds crRNA and forms the helical backbone of Cascade. Many archaea encode a version of the Cascade complex (denoted Type I-A) that includes a Csa5 (or small) subunit, which interacts weakly with the core proteins. Here, we report the crystal structure of the Csa5 protein from Sulfolobus solfataricus. Csa5 comprises a conserved α-helical domain with a small insertion consisting of a weakly conserved β-strand domain. In the crystal, the Csa5 monomers have multimerized into infinite helical threads. At each interface is a strictly conserved intersubunit salt bridge, deletion of which disrupts multimerization. Structural analysis indicates a shared evolutionary history among the small subunits of the CRISPR effector complexes. The same α-helical domain is found in the C-terminal domain of Cse2 (from Type I-E Cascade), while the N-terminal domain of Cse2 is found in Cmr5 of the CMR (Type III-B) effector complex. As Cmr5 shares no match with Csa5, two possibilities present themselves: selective domain loss from an ancestral Cse2 to create two new subfamilies or domain fusion of two separate families to create a new Cse2 family. A definitive answer awaits structural studies of further small subunits from other CRISPR effector complexes.