清华大学刘俊杰等研究人员合作开发出用于增强细菌免疫力的Pro-CRISPR PcrIIC1相关Cas9系统。该项研究成果于2024年5月29日在线发表在《自然》杂志上。

研究人员确定了2062个完整的Cas9基因座，预测了其相关蛋白的结构，并揭示了II-C型Cas9的三种结构生长轨迹。研究人员发现，新的相关基因（NAG）往往存在于较大的II-C Cas9的基因座中。进一步研究发现，来自Chryseobacterium物种的CbCas9含有一个新的β-REC2结构域，并与NAG编码的II-CCas9 的CRISPR-Cas系统促进蛋白（pro-CRISPR）（PcrIIC1）形成异源四聚体复合物。

与独立的CbCas9相比，CbCas9-PcrIIC1复合物具有更强的DNA结合力和切割活性，对原间隔相邻基序的兼容性更广，对错配的耐受力更强，抗噬菌体免疫力更高。总之，该研究揭示了II-C Cas9蛋白在结构水平上的多样性和“生长演化”轨迹，并发现了许多NAG，如PcrIIC1，它是一种支持CRISPR的因子，可增强CRISPR介导的免疫力。

据介绍，CRISPR系统是原核生物中的一种适应性免疫系统，可抵御外来DNA入侵宿主细胞。在噬菌体与细菌免疫系统的持续斗争中，CRISPR系统演化成了多种类型，每种类型都具有不同的功能。II型Cas9是这些系统中研究最为广泛的一种，具有多种亚型。目前仍不确定该家族成员是否能演化出其他机制来对抗病毒入侵。

附：英文原文

Title: Pro-CRISPR PcrIIC1-associated Cas9 system for enhanced bacterial immunity

Author: Zhang, Shouyue, Sun, Ao, Qian, Jing-Mei, Lin, Shuo, Xing, Wenjing, Yang, Yun, Zhu, Han-Zhou, Zhou, Xin-Yi, Guo, Yan-Shuo, Liu, Yun, Meng, Yu, Jin, Shu-Lin, Song, Wenhao, Li, Cheng-Ping, Li, Zhaofu, Jin, Shuai, Wang, Jian-Hua, Dong, Meng-Qiu, Gao, Caixia, Chen, Chunlai, Bai, Yang, Liu, Jun-Jie Gogo

Issue&Volume: 2024-05-29

Abstract: The CRISPR system is an adaptive immune system found in prokaryotes that defends host cells against the invasion of foreign DNA1. As part of the ongoing struggle between phages and the bacterial immune system, the CRISPR system has evolved into various types, each with distinct functionalities2. Type II Cas9 is the most extensively studied of these systems and has diverse subtypes. It remains uncertain whether members of this family can evolve additional mechanisms to counter viral invasions3,4. Here we identify 2,062 complete Cas9 loci, predict the structures of their associated proteins and reveal three structural growth trajectories for type II-C Cas9. We found that novel associated genes (NAGs) tended to be present within the loci of larger II-C Cas9s. Further investigation revealed that CbCas9 from Chryseobacterium species contains a novel β-REC2 domain, and forms a heterotetrameric complex with an NAG-encoded CRISPR–Cas-system-promoting (pro-CRISPR) protein of II-C Cas9 (PcrIIC1). The CbCas9–PcrIIC1 complex exhibits enhanced DNA binding and cleavage activity, broader compatibility for protospacer adjacent motif sequences, increased tolerance for mismatches and improved anti-phage immunity, compared with stand-alone CbCas9. Overall, our work sheds light on the diversity and ‘growth evolutionary’ trajectories of II-C Cas9 proteins at the structural level, and identifies many NAGs—such as PcrIIC1, which serves as a pro-CRISPR factor to enhance CRISPR-mediated immunity.

DOI: 10.1038/s41586-024-07486-x

Source: https://www.nature.com/articles/s41586-024-07486-x