PDF(Pubmed)
Abstract：
CRISPR-Cas systems are known to be part of the bacterial adaptive immune system that provides resistance against intruders such as viruses, phages and other mobile genetic elements. To combat this bacterial defense mechanism, phages encode inhibitors called Acrs (anti-CRISPR proteins) that can suppress them. AcrIC9 is the most recently identified member of the AcrIC family that inhibits the type IC CRISPR-Cas system. Here, the crystal structure of AcrIC9 from Rhodobacter capsulatus is reported, which comprises a novel fold made of three central antiparallel β-strands surrounded by three α-helixes, a structure that has not been detected before. It is also shown that AcrIC9 can form a dimer via disulfide bonds generated by the Cys69 residue. Finally, it is revealed that AcrIC9 directly binds to the type IC cascade. Analysis and comparison of its structure with structural homologs indicate that AcrIC9 belongs to DNA-mimic Acrs that directly bind to the cascade complex and hinder the target DNA from binding to the cascade.
摘要：
已知CRISPR-Cas系统是细菌适应性免疫系统的一部分，可提供对病毒等入侵者的抗性。噬菌体和其他可移动的遗传元件。为了对抗这种细菌防御机制，噬菌体编码称为Acrs（抗CRISPR蛋白）的抑制剂，可以抑制它们。AcrIC9是抑制ICCRISPR-Cas型系统的AcrIC家族的最新鉴定的成员。这里,据报道，胶囊红杆菌属AcrIC9的晶体结构，它包括由三个α螺旋围绕的三个中央反平行β链组成的新折叠，以前没有检测到的结构。还显示AcrIC9可以通过Cys69残基产生的二硫键形成二聚体。最后,揭示了AcrIC9直接结合到IC型级联。其结构与结构同源物的分析和比较表明AcrIC9属于DNA模拟Acrs,其直接结合级联复合物并阻碍靶DNA结合级联。
