Structure of a dimeric crenarchaeal Cas6 enzyme with an atypical active site for CRISPR RNA processing.
Structure of a dimeric crenarchaeal Cas6 enzyme with an atypical active site for CRISPR RNA processing.
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DOI：
10.1042/bj20130269
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发表时间：
2013-06-01
期刊：
影响因子：
--
通讯作者：
White MF
中科院分区：
文献类型：
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作者：
Reeks J;Sokolowski RD;Graham S;Liu H;Naismith JH;White MF
病毒和宿主之间的竞争在生命的各个分支中都有。许多原核生物具有称为“CRISPR”（成簇的规则间隔的短回文重复序列）的适应性免疫系统，其基于捕获病毒DNA的短片段。捕获的DNA被整合到生物体的基因组DNA中，侧翼是同向重复序列，转录并加工以产生crRNA（CRISPR RNA），其被加载到各种效应复合物中。这些复合物对入侵的移动的遗传元件进行序列特异性检测和破坏。在本文中，我们报告了来自硫磺硫化叶菌的Cas6（CRISPR相关6）酶（Sso1437）的结构和活性，该酶负责产生单位长度的crRNA种类。晶体结构揭示了一个不寻常的二聚体组织，这对酶的活性很重要。此外，活性位点缺乏已被视为Cas6家族的基本特征的典型催化组氨酸残基。虽然有几个残基有助于催化，但没有一个是绝对必要的。再加上Cas6家族非常低的催化速率常数和活性位点的可塑性，这表明Cas6家族的crRNA识别和分子伴侣样活性应被认为与它们作为传统酶的作用相同或甚至更重要。
The competition between viruses and hosts is played out in all branches of life. Many prokaryotes have an adaptive immune system termed ‘CRISPR’ (clustered regularly interspaced short palindromic repeats) which is based on the capture of short pieces of viral DNA. The captured DNA is integrated into the genomic DNA of the organism flanked by direct repeats, transcribed and processed to generate crRNA (CRISPR RNA) that is loaded into a variety of effector complexes. These complexes carry out sequence-specific detection and destruction of invading mobile genetic elements. In the present paper, we report the structure and activity of a Cas6 (CRISPR-associated 6) enzyme (Sso1437) from Sulfolobus solfataricus responsible for the generation of unit-length crRNA species. The crystal structure reveals an unusual dimeric organization that is important for the enzyme's activity. In addition, the active site lacks the canonical catalytic histidine residue that has been viewed as an essential feature of the Cas6 family. Although several residues contribute towards catalysis, none is absolutely essential. Coupled with the very low catalytic rate constants of the Cas6 family and the plasticity of the active site, this suggests that the crRNA recognition and chaperone-like activities of the Cas6 family should be considered as equal to or even more important than their role as traditional enzymes.