By targeting key regulatory hubs of their host, bacteriophages represent a powerful source for the identification of novel antimicrobial proteins. Here, a screening of small cytoplasmic proteins encoded by the CGP3 prophage of Corynebacterium glutamicum resulted in the identification of the gyrase-inhibiting protein Cg1978, termed Gip. Pull-down assays and surface plasmon resonance revealed a direct interaction of Gip with the gyrase subunit A (GyrA). The inhibitory activity of Gip was shown to be specific to the DNA gyrase of its bacterial host C. glutamicum. Overproduction of Gip in C. glutamicum resulted in a severe growth defect as well as an induction of the SOS response. Furthermore, reporter assays revealed an RecA-independent induction of the cryptic CGP3 prophage, most likely caused by topological alterations. Overexpression of gip was counteracted by an increased expression of gyrAB and a reduction of topA expression at the same time, reflecting the homeostatic control of DNA topology. We postulate that the prophage-encoded Gip protein plays a role in modulating gyrase activity to enable efficient phage DNA replication. A detailed elucidation of the mechanism of action will provide novel directions for the design of drugs targeting DNA gyrase.

中文翻译：

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Gip作为一种新型噬菌体编码的谷氨酸棒杆菌促旋酶抑制剂蛋白的鉴定

通过靶向宿主的关键调控中心，噬菌体代表了鉴定新型抗菌蛋白的强大来源。在这里，对谷氨酸棒杆菌CGP3 前噬菌体编码的小细胞质蛋白的筛选导致鉴定了Gyrase抑制蛋白Cg1978，称为 Gip 。下拉测定和表面等离子共振揭示了 Gip 与旋转酶亚基 A (GyrA) 的直接相互作用。Gip 的抑制活性被证明对其细菌宿主谷氨酸棒杆菌的 DNA 促旋酶具有特异性。谷氨酸棒杆菌中 Gip 的过量生产导致严重的生长缺陷以及SOS反应的诱导。此外，报告基因分析揭示了一种不依赖 RecA 的隐蔽 CGP3 前噬菌体诱导，这很可能是由拓扑改变引起的。gip的过度表达被gyrAB的表达增加和topA表达的减少同时抵消，这反映了 DNA 拓扑结构的稳态控制。我们假设前噬菌体编码的 Gip 蛋白在调节旋转酶活性以实现高效的噬菌体 DNA 复制中发挥作用。详细阐明作用机制将为设计靶向 DNA 促旋酶的药物提供新的方向。