Nasrallah Gheyath K, Abdelhady Hany, Tompkins Nicholas P, Carson Kaitlyn R, Garduño Rafael A
Department of Health Sciences, Biomedical Sciences Program, College of Arts and Sciences, Qatar University, Doha, Qatar.
Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada.
Int J Med Microbiol. 2014 Jul;304(5-6):703-16. doi: 10.1016/j.ijmm.2014.05.004. Epub 2014 May 15.
L. pneumophila is an intracellular pathogen that replicates in a membrane-bound compartment known as the Legionella-containing vacuole (LCV). We previously observed that the polyamine spermidine, produced by host cells or added exogenously, enhances the intracellular growth of L. pneumophila. To study this enhancing effect and determine whether polyamines are used as nutrients, we deleted potD from L. pneumophila strain JR32. The gene potD encodes a spermidine-binding protein that in other bacteria is essential for the function of the PotABCD polyamine transporter. Deletion of potD did not affect L. pneumophila growth in vitro in the presence or absence of spermidine and putrescine, suggesting that PotD plays a redundant or no role in polyamine uptake. However, deletion of potD resulted in a puzzlingly complex phenotype that included defects in L. pneumophila's ability to form filaments, tolerate Na(+), associate with macrophages and amoeba, recruit host vesicles to the LCV, and initiate intracellular growth. Moreover, the ΔpotD mutant was completely unable to grow in L929 cells treated with a pharmacological inhibitor of spermidine synthesis. These complex and disparate effects suggest that the L. pneumophila potD encodes either: (i) a multifunctional protein, (ii) a protein that interacts with, or regulates a, multifunctional protein, or (iii) a protein that contributes (directly or indirectly) to a regulatory network. Protein function studies with the L. pneumophila PotD protein are thus warranted.
嗜肺军团菌是一种细胞内病原体，在称为含军团菌液泡（LCV）的膜结合区室中进行复制。我们之前观察到，由宿主细胞产生或外源添加的多胺亚精胺可增强嗜肺军团菌的细胞内生长。为了研究这种增强作用并确定多胺是否被用作营养物质，我们从嗜肺军团菌菌株JR32中删除了potD基因。potD基因编码一种亚精胺结合蛋白，在其他细菌中，该蛋白对于PotABCD多胺转运蛋白的功能至关重要。在有或没有亚精胺和腐胺的情况下，删除potD并不影响嗜肺军团菌在体外的生长，这表明PotD在多胺摄取中起冗余作用或不起作用。然而，删除potD导致了一个令人困惑的复杂表型，包括嗜肺军团菌形成丝状的能力、耐受Na⁺的能力、与巨噬细胞和变形虫结合的能力、将宿主囊泡募集到LCV的能力以及启动细胞内生长的能力存在缺陷。此外，ΔpotD突变体在用亚精胺合成的药理抑制剂处理的L929细胞中完全无法生长。这些复杂且不同的效应表明，嗜肺军团菌potD编码的要么是：（i）一种多功能蛋白，（ii）一种与多功能蛋白相互作用或调节多功能蛋白的蛋白，要么是（iii）一种（直接或间接）对调节网络有贡献的蛋白。因此，有必要对嗜肺军团菌PotD蛋白进行蛋白质功能研究。
