Wassarman Douglas R, Pfaff Patrick, Paulo Joao A, Gygi Steven P, Shokat Kevan M, Kranzusch Philip J
bioRxiv. 2025 Apr 6:2025.04.06.647259. doi: 10.1101/2025.04.06.647259.
7-deazapurines are nucleobase analogs essential for nucleic acid modifications in nearly all cellular life. Here, we discover a role for 7-deazapurines in protein modification within type IV CBASS anti-phage defense and define functions for CBASS ancillary proteins Cap9 and Cap10 in nucleobase-protein conjugation. A structure of Cap10 reveals a tRNA transglycosylase-family enzyme remodeled to bind the modified N-terminus of a partner cGAS/DncV-like nucleotidyltransferase linked to a 7-amido-7-deazaguanine (NDG) nucleobase. The structure of Cap9 explains how this QueC-like enzyme co-opts a 7-deazapurine biosynthetic reaction mechanism for NDG conjugation. We demonstrate that Cap9, Cap10, and NDG conjugation are essential for host defense against phage infection. Our results define a previously unknown 7-deazapurine protein modification and explain how nucleobase biosynthetic machinery has been repurposed for antiviral immunity.
7-脱氮嘌呤是几乎所有细胞生命中核酸修饰所必需的核碱基类似物。在这里，我们发现了7-脱氮嘌呤在IV型CBASS抗噬菌体防御中的蛋白质修饰作用，并确定了CBASS辅助蛋白Cap9和Cap10在核碱基-蛋白质缀合中的功能。Cap10的结构揭示了一种tRNA转糖基酶家族酶经过重塑，以结合与7-氨基-7-脱氮鸟嘌呤（NDG）核碱基相连的伴侣cGAS/DncV样核苷酸转移酶的修饰N端。Cap9的结构解释了这种类似QueC的酶如何采用7-脱氮嘌呤生物合成反应机制进行NDG缀合。我们证明Cap9、Cap10和NDG缀合对于宿主抵抗噬菌体感染至关重要。我们的结果定义了一种以前未知的7-脱氮嘌呤蛋白质修饰，并解释了核碱基生物合成机制如何被重新用于抗病毒免疫。
