Gao Angela, Wassarman Douglas R, Kranzusch Philip J
Department of Microbiology, Harvard Medical School, Boston, MA 02115, USA.
Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, MA 02115, USA.
bioRxiv. 2025 Sep 3:2025.09.03.674047. doi: 10.1101/2025.09.03.674047.
QueC proteins are nucleoside biosynthesis enzymes required for production of the 7-deazaguanine derivative queuosine. Recently, QueC-family proteins were also shown to catalyze a deazaguanylation protein-nucleobase conjugation reaction in type IV CBASS bacterial anti-phage defense. Here we determine the structural basis of QueC-family protein function in a distinct bacterial immunity system named qatABCD. We demonstrate that the QueC-family protein QatC forms a specific complex with the immunity protein QatB and that this complex is minimally required for qatABCD defense. Crystal structures of the QatBC complex enable direct comparison of qatABCD and type IV CBASS defense and support a shared role for QueC-family proteins in targeting protein substrates for N-terminal modification. We show that the QatB unstructured N-terminus and N-terminal glycine motif are essential for qatABCD defense , suggesting a modification occurs analogous to CBASS deazaguanylation. These findings highlight broad roles of QueC proteins beyond nucleoside biosynthesis and suggest that adaptation of QueC-like proteins for specialized biochemical functions is a common strategy in bacterial anti-phage immunity.
QueC蛋白是合成7-脱氮鸟嘌呤衍生物queuosine所需的核苷生物合成酶。最近，QueC家族蛋白还被证明在IV型CBASS细菌抗噬菌体防御中催化脱氮鸟苷酸化蛋白-核碱基共轭反应。在这里，我们确定了QueC家族蛋白在一个名为qatABCD的独特细菌免疫系统中的功能结构基础。我们证明，QueC家族蛋白QatC与免疫蛋白QatB形成特定复合物，并且该复合物是qatABCD防御所必需的最低限度成分。QatBC复合物的晶体结构能够直接比较qatABCD和IV型CBASS防御，并支持QueC家族蛋白在靶向蛋白质底物进行N端修饰方面的共同作用。我们表明，QatB的无结构N端和N端甘氨酸基序对于qatABCD防御至关重要，这表明发生了类似于CBASS脱氮鸟苷酸化的修饰。这些发现突出了QueC蛋白在核苷生物合成之外的广泛作用，并表明将QueC样蛋白适应特殊生化功能是细菌抗噬菌体免疫中的一种常见策略。
