美国洛克菲勒大学Luciano A. Marraffini和美国纪念斯隆-凯特琳癌症中心Dinshaw J. Patel团队共同合作，近期取得重要进展。他们研究提出，CRISPR相关腺苷脱氨酶Cad1通过将ATP转化为ITP来提供抗病毒免疫力。相关研究成果2024年10月28日在线发表于《细胞》杂志上。
据介绍，III型CRISPR系统通过产生环状寡腺苷酸（cAn）分子来提供对遗传入侵者的免疫力，这些分子激活含有CRISPR相关Rossman折叠（CARF）结构域的效应蛋白。
研究人员表征了CARF结构域与腺苷脱氨酶结构域融合的效应物的功能和结构，CRISPR相关腺苷脱氨酶酶1（Cad1）。研究人员发现，在cA4或cA6与其CARF结构域结合后，Cad1在体内和体外均可将ATP转化为ITP。
全长Cad1的冷冻电镜（cryo-EM）结构研究，揭示了一个由二聚体和三聚体组成的六聚体组装体，在活性所需的结构域间位点结合了ATP，在脱氨酶活性位点内结合了ATP/ITP。在噬菌体感染期间合成cAn后，Cad1激活导致宿主生长停滞，从而阻止病毒繁殖。
总之，这一研究结果表明，CRISPR-Cas系统利用核酸降解以外的广泛分子机制，在原核生物中提供适应性免疫。
附：英文原文
Title: The CRISPR-associated adenosine deaminase Cad1 converts ATP to ITP to provide antiviral immunity
Author: Christian F. Baca, Puja Majumder, James H. Hickling, Linzhi Ye, Marianna Teplova, Sean F. Brady, Dinshaw J. Patel, Luciano A. Marraffini
Issue&Volume: 2024-10-28
Abstract: Type III CRISPR systems provide immunity against genetic invaders through the production of cyclic oligo-adenylate (cAn) molecules that activate effector proteins that contain CRISPR-associated Rossman fold (CARF) domains. Here, we characterized the function and structure of an effector in which the CARF domain is fused to an adenosine deaminase domain, CRISPR-associated adenosine deaminase 1 (Cad1). We show that upon binding of cA4 or cA6 to its CARF domain, Cad1 converts ATP to ITP, both in vivo and in vitro. Cryoelectron microscopy (cryo-EM) structural studies on full-length Cad1 reveal an hexameric assembly composed of a trimer of dimers, with bound ATP at inter-domain sites required for activity and ATP/ITP within deaminase active sites. Upon synthesis of cAn during phage infection, Cad1 activation leads to a growth arrest of the host that prevents viral propagation. Our findings reveal that CRISPR-Cas systems employ a wide range of molecular mechanisms beyond nucleic acid degradation to provide adaptive immunity in prokaryotes.
DOI: 10.1016/j.cell.2024.10.002
Source: https://www.cell.com/cell/abstract/S0092-8674(24)01150-4