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VirK family [Pfam06903] consists of 14 bacterial VirK proteins of around 145 residues in length. The function of this family is unknown. Herein, using single-wavelength anomalous diffraction, we determined the crystal structure of lpg1832, a VirK family protein from Legionella pneumophila, at 2.0 Å resolution. This is the first structural determination of a VirK domain-containing protein. Lpg1832 is a type II secretion system-dependent extracellular protein that folds into a novel barrel-shaped structure. It is found to adopt a quaternary assembly comprising a homotetramer. The three-dimensional structure of lpg1832 provides the first structural information pertaining to the VirK family and allows us to possibly identify its functionally important regions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Legionella pneumophila type II secretion system can promote bacterial growth under a wide variety of conditions and mediates the secretion of more than 25 proteins, including the uncharacterized effector Lpg2622. Here, we determined the crystal structures of apo‐Lpg2622 and Lpg2622 in complex with the cysteine protease inhibitor E64. Structural analysis suggests that Lpg2622 belongs to the C1 family peptidases. Interestingly, unlike the other structurally resolved papain‐like cysteine proteases, the propeptide of Lpg2622 forms a novel super‐secondary structural fold (hairpin‐turn‐helix) and can be categorized into a new group. In addition, the N‐terminal β‐sheet of the Lpg2622 propeptide plays a regulatory role on enzymatic activity. This study enhances our understanding of the classification and regulatory mechanisms of the C1 family peptidases. [ABSTRACT FROM AUTHOR]

The major acid phosphatase from Legionella pneumophila ( LpMAP) belongs to the histidine acid phosphatase superfamily. It contains the characteristic histidine acid phosphatase (HAP) sequence motif RHG XR XP responsible for the hydrolysis of a phosphoryl group from phosphate monoesters under acidic conditions. Here, the crystallization and preliminary X-ray analysis of crystals of LpMAP in the apo form and in complex with L-(+)-tartrate are described. By using the hanging-drop vapour-diffusion method, apo LpMAP and LpMAP-tartrate were crystallized in space group P21, with unit-cell parameters a = 91.50, b = 56.48, c = 146.35 Å, β = 110.01°, and in space group P1, with unit-cell parameters a = 55.51, b = 73.51 , c = 98.78 Å, α = 78.82, β = 77.65, γ = 67.73°, respectively. Diffraction data were collected at 100 K and the phases were determined using the molecular-replacement method. [ABSTRACT FROM AUTHOR]