美国洛克菲勒大学Luciano A. Marraffini和斯隆·凯特琳纪念癌症中心Dinshaw J. Patel小组合作发现，Card1核酸酶在III型CRISPR免疫过程中提供保护。相关论文于2021年1月18日在线发表在《自然》杂志上。

研究人员探究了III型CRISPR辅助蛋白Card1的功能。Card1形成一个对称的二聚体，在其CARF和结合cA4限制性核酸内切酶（REase）结构域之间形成一个大的中心腔。配体结合导致构象变化，其中单个单体彼此相对旋转以形成更紧凑的二聚体支架，其中阳离子Mn与催化残基配位并导致单链而非双链核酸（DNA和RNA）裂解。在体内，Card1激活诱导感染宿主休眠，从而提供了针对噬菌体感染和质粒的免疫。

该结果揭示了CRISPR系统在提供免疫过程中的功能多样性。

据介绍，在原核生物III型CRISPR-Cas免疫反应过程中，感染会造成环状寡聚腺苷酸的产生，后者结合并激活含有CARF结构域的蛋白质。许多III型基因座与蛋白质相关，其中CARF结构域与核酸内切酶样结构域融合。但是，除了已知的Csm6/Csx1 RNases外，尚不清楚这些诱导型效应因子是否以及如何提供防御。

附：英文原文

Title: The Card1 nuclease provides defence during type-III CRISPR immunity

Author: Jakob T. Rostl, Wei Xie, Vitaly Kuryavyi, Pascal Maguin, Kevin Kao, Ruby Froom, Dinshaw J. Patel, Luciano A. Marraffini

Issue&Volume: 2021-01-18

Abstract: During the prokaryotic type III CRISPR-Cas immune response, infection triggers the production of cyclic oligoadenylates, which bind and activate CARF domain-containing proteins1,2. Many type III loci are associated with proteins in which the CARF domain is fused to an endonuclease-like domain3,4; however, with the exception of the well-characterized Csm6/Csx1 RNases5,6, whether and how these inducible effectors provide defense is not known. Here we investigated one of such type III CRISPR accessory proteins, Card1. Card1 forms a symmetrical dimer with a large central cavity between its CARF and restriction endonuclease (REase) domains that binds cA4. Ligand binding results in a conformational change where individual monomers rotate relative to each other to form a more compact dimeric scaffold wherein a Mn cation coordinates to the catalytic residues and activates the cleavage of single, but not double, stranded nucleic acids (DNA and RNA). In vivo, Card1 activation induces dormancy of the infected hosts to provide immunity against phage infection and plasmids. Our results highlight the diversity of strategies used by CRISPR systems to provide immunity.

DOI: 10.1038/s41586-021-03206-x

Source: https://www.nature.com/articles/s41586-021-03206-x