Abstract：
CRISPR-Cas systems confer adaptive immunity in prokaryotes, facilitating the recognition and destruction of invasive nucleic acids. Type III CRISPR systems comprise large, multisubunit ribonucleoprotein complexes with a catalytic Cas10 subunit. When activated by the detection of foreign RNA, Cas10 generates nucleotide signalling molecules that elicit an immune response by activating ancillary effector proteins. Among these systems, the Bacteroides fragilis type III CRISPR system was recently shown to produce a novel signal molecule, SAM-AMP, by conjugating ATP and SAM. SAM-AMP regulates a membrane effector of the CorA family to provide immunity. Here, we focus on NYN, a ribonuclease encoded within this system, probing its potential involvement in crRNA maturation. Structural modelling and in vitro ribonuclease assays reveal that NYN displays robust sequence-nonspecific, Mn2+-dependent ssRNA-cleavage activity. Our findings suggest a role for NYN in trimming crRNA intermediates into mature crRNAs, which is necessary for type III CRISPR antiviral defence. This study sheds light on the functional relevance of CRISPR-associated NYN proteins and highlights the complexity of CRISPR-mediated defence strategies in bacteria.
摘要：
CRISPR-Cas系统在原核生物中赋予适应性免疫，促进侵入性核酸的识别和破坏。III型CRISPR系统包括大型，具有催化Cas10亚基的多亚基核糖核蛋白复合物。当通过检测外源RNA激活时，Cas10产生核苷酸信号分子,其通过激活辅助效应蛋白引发免疫应答。在这些系统中，脆弱拟杆菌III型CRISPR系统最近被证明可以产生一种新的信号分子，SAM-AMP,通过缀合ATP和SAM。SAM-AMP调节CorA家族的膜效应物以提供免疫力。这里,我们专注于NYN，在这个系统中编码的核糖核酸酶，探索其在crRNA成熟中的潜在参与。结构建模和体外核糖核酸酶测定表明，NYN表现出强大的序列非特异性，Mn2+依赖性ssRNA切割活性。我们的发现表明NYN在将crRNA中间体修剪成成熟crRNA中的作用，这是III型CRISPR抗病毒防御所必需的。这项研究揭示了CRISPR相关NYN蛋白的功能相关性，并强调了CRISPR介导的细菌防御策略的复杂性。
