Legionella pneumophila encodes an extracellular secreted phospholipase A named PlaA that is translocated by the type II secretion system. It plays an essential role in maintaining the integrity of Legionella‐containing vacuoles in L. pneumophila pathogenesis. Here, it is shown that PlaA has a main lysophospholipase activity to hydrolyze fatty‐acyl groups in lysophospholipids. Although it has a very low phospholipase A activity to catalyze the hydrolysis of fatty‐acyl groups in phospholipids, PlaA can bind phospholipids such as 1,2‐dipalmitoylphosphatidylcholine with a dissociation constant of 11.1 µM. Sequence‐alignment analysis combined with activity assays revealed that PlaA contains a distinct substrate‐binding site among the known structures of the phospholipase A family, implying that PlaA may present a novel mechanism for substrate recognition. Native PlaA and its selenomethionine (SeMet)‐substituted form were purified and crystallized by vapour diffusion in hanging drops at 296 K. Diffraction data were collected to a resolution of 2.0 Å for native PlaA protein and to a resolution of 2.7 Å for SeMet‐substituted PlaA protein. The crystals of native PlaA belonged to the monoclinic space group P2₁, while the crystals of SeMet‐substituted PlaA belonged to the primitive orthorhombic space group P2₁2₁2₁. Initial phases for PlaA were obtained from SeMet SAD data sets.

中文翻译：

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嗜肺军团菌的磷脂酶A效应物PlaA：表达，纯化和结晶。

嗜肺军团菌编码一种被称为IIA分泌系统的易位胞外分泌磷脂酶A。它在维持嗜肺军团菌发病机理中包含军团菌的液泡的完整性中起着至关重要的作用。在此表明，PlaA具有主要的溶血磷脂酶活性，可水解溶血磷脂中的脂肪酰基。尽管它具有极低的磷脂酶A催化磷脂中脂肪酰基水解的活性，但PlaA可以结合磷脂，例如1,2-二棕榈酰磷脂酰胆碱，其解离常数为11.1 µ M。序列比对分析与活性分析相结合发现，PlaA在磷脂酶A家族的已知结构中包含一个独特的底物结合位点，这表明PlaA可能提供了一种新型的底物识别机制。天然PlaA及其硒代甲硫氨酸（SeMet）取代的形式经过纯化，并通过在296 K的悬滴中通过蒸汽扩散进行结晶。对于天然PlaA蛋白，衍射数据的分辨率为2.0Å，对于SeMet取代的分辨率为2.7Å PlaA蛋白。天然PlaA的晶体属于单斜晶空间群P 2 ₁，而SeMet取代的PlaA的晶体属于原始正交晶空间群P 2 ₁ 2 ₁ 2。₁。从SeMet SAD数据集获得PlaA的初始阶段。