The pathogen Legionella pneumophila, which is the causative agent of Legionnaires' disease, secrets hundreds of effectors into host cells via its Dot/Icm secretion system to subvert host-cell pathways during pathogenesis. VipF, a conserved core effector among Legionella species, is a putative acetyltransferase, but its structure and catalytic mechanism remain unknown. Here, three crystal structures of VipF in complex with its cofactor acetyl-CoA and/or a substrate are reported. The two GNAT-like domains of VipF are connected as two wings by two β-strands to form a U-shape. Both domains bind acetyl-CoA or CoA, but only in the C-terminal domain does the molecule extend to the bottom of the U-shaped groove as required for an active transferase reaction; the molecule in the N-terminal domain folds back on itself. Interestingly, when chloramphenicol, a putative substrate, binds in the pocket of the central U-shaped groove adjacent to the N-terminal domain, VipF remains in an open conformation. Moreover, mutations in the central U-shaped groove, including Glu129 and Asp251, largely impaired the acetyltransferase activity of VipF, suggesting a unique enzymatic mechanism for the Legionella effector VipF.

中文翻译：

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军团菌效应子 VipF 乙酰化机制的结构基础

病原体嗜肺军团菌是军团病的病原体，它通过其 Dot/Icm 分泌系统将数百种效应物分泌到宿主细胞中，从而在发病过程中破坏宿主细胞通路。VipF，军团菌中保守的核心效应器种，是一种推定的乙酰转移酶，但其结构和催化机制仍然未知。在这里，报道了与其辅因子乙酰辅酶 A 和/或底物复合的 VipF 的三种晶体结构。VipF 的两个 GNAT 样结构域通过两个 β 链连接为两个翼，形成 U 形。两个结构域都结合乙酰辅酶A或辅酶A，但只有在C末端结构域中，分子才会根据活性转移酶反应的需要延伸到U形凹槽的底部；N端结构域中的分子会自行折叠。有趣的是，当假定的底物氯霉素结合在与 N 末端结构域相邻的中央 U 形凹槽的口袋中时，VipF 保持开放构象。此外，中央 U 形凹槽中的突变，包括 Glu129 和 Asp251，军团菌效应器 VipF。