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Abstract：
Legionella pneumophila and other Legionella species replicate intracellularly using the Icm/Dot type IV secretion system. In L. pneumophila this system translocates >300 effectors into host cells and in the Legionella genus thousands of effectors were identified, the function of most of which is unknown. Fourteen L. pneumophila effectors were previously shown to specifically bind phosphoinositides (PIs) using dedicated domains. We found that PI-binding domains of effectors are usually not homologous to one another; they are relatively small and located at the effectors\' C termini. We used the previously identified Legionella effector domains (LEDs) with unknown function and the above characteristics of effector PI-binding domains to discover novel PI-binding LEDs. We identified three predicted PI-binding LEDs that are present in 14 L. pneumophila effectors and in >200 effectors in the Legionella genus. Using an in vitro protein-lipid overlay assay, we found that 11 of these L. pneumophila effectors specifically bind phosphatidylinositol 3-phosphate (PI3P), almost doubling the number of L. pneumophila effectors known to bind PIs. Further, we identified in each of these newly discovered PI3P-binding LEDs conserved, mainly positively charged, amino acids that are essential for PI3P binding. Our results indicate that Legionella effectors harbor unique domains, shared by many effectors, which directly mediate PI3P binding.
摘要：
嗜肺军团菌和其他军团菌使用Icm/DotIV型分泌系统在细胞内复制。在嗜肺乳杆菌中，该系统可将>300个效应子转移到宿主细胞中，在军团菌属中，鉴定出数千种效应子，其中大部分的功能是未知的。先前显示十四种嗜肺乳杆菌效应子使用专用结构域特异性结合磷酸肌醇(PI)。我们发现效应子的PI结合域通常彼此不同源；它们相对较小，位于效应子的C末端。我们使用先前鉴定的具有未知功能的军团菌效应子结构域（LED）和效应子PI结合结构域的上述特征来发现新型PI结合LED。我们确定了三种预测的PI结合LED，它们存在于14个嗜肺乳杆菌效应子和军团菌属的>200个效应子中。使用体外蛋白质-脂质覆盖测定法，我们发现这些嗜肺乳杆菌效应子中有11种特异性结合磷脂酰肌醇3-磷酸（PI3P），已知与PI结合的嗜肺乳杆菌效应物的数量几乎翻了一番。Further,我们发现，在这些新发现的PI3P结合LED中，主要带正电荷，PI3P结合所必需的氨基酸。我们的结果表明，军团菌效应子具有独特的结构域，由许多效应器共享，直接介导PI3P结合。
