Biomedicine Discovery Institute, Department of Microbiology, Monash University, Clayton, VIC, Australia.
Centre to Impact AMR, Monash University, Clayton, VIC, Australia.
Nat Commun. 2024 Oct 8;15(1):8709. doi: 10.1038/s41467-024-52950-x.
The type VI secretion system (T6SS) is a molecular machine utilised by many Gram-negative bacteria to deliver antibacterial toxins into adjacent cells. Here we present the structure of Tse15, a T6SS Rhs effector from the nosocomial pathogen Acinetobacter baumannii. Tse15 forms a triple layered β-cocoon Rhs domain with an N-terminal α-helical clade domain and an unfolded C-terminal toxin domain inside the Rhs cage. Tse15 is cleaved into three domains, through independent auto-cleavage events involving aspartyl protease activity for toxin self-cleavage and a nucleophilic glutamic acid for N-terminal clade cleavage. Proteomic analyses identified that significantly more peptides from the N-terminal clade and toxin domains were secreted than from the Rhs cage, suggesting toxin delivery often occurs without the cage. We propose the clade domain acts as an internal chaperone to mediate toxin tethering to the T6SS machinery. Conservation of the clade domain in other Gram-negative bacteria suggests this may be a common mechanism for delivery.
VI 型分泌系统（T6SS）是一种分子机器，许多革兰氏阴性菌利用它将抗菌毒素输送到相邻的细胞中。在这里，我们展示了医院病原体鲍曼不动杆菌的 T6SS Rhs 效应物 Tse15 的结构。Tse15 形成了一个三层的β-cocoon Rhs 结构域，其 N 端有一个α-螺旋 clade 结构域，内部有一个未折叠的 C 端毒素结构域。Tse15 通过三个独立的自切割事件被切割成三个结构域，这些事件涉及天冬氨酸蛋白酶活性的毒素自我切割和亲核谷氨酸的 N 端 clade 切割。蛋白质组学分析表明，从 N 端 clade 和毒素结构域分泌的肽明显多于从 Rhs 笼中分泌的肽，这表明毒素输送通常在没有笼子的情况下发生。我们提出，clade 结构域充当内部伴侣，介导毒素与 T6SS 机器的连接。其他革兰氏阴性菌中 clade 结构域的保守性表明，这可能是一种常见的输送机制。
