Phosphoinositide-mediated oligomerization of a defensin induces cell lysis.
Phosphoinositide-mediated oligomerization of a defensin induces cell lysis.
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DOI：
10.7554/elife.01808
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发表时间：
2014-04-01
期刊：
影响因子：
7.7
通讯作者：
Hulett MD
中科院分区：
文献类型：
--
作者：
Poon IKh;Baxter AA;Lay FT;Mills GD;Adda CG;Payne JA;Phan TK;Ryan GF;White JA;Veneer PK;van der Weerden NL;Anderson MA;Kvansakul M;Hulett MD
阳离子抗微生物肽（CAPs）如防御素是普遍存在的先天免疫分子，其通常表现出对微生物病原体和哺乳动物肿瘤细胞的广泛活性。许多CAP作用于细胞的质膜，导致膜不稳定和透化。在这项研究中，我们描述了一种新的细胞裂解机制，真菌和肿瘤细胞的植物防御素NaD 1的作用，通过直接结合到质膜磷脂磷脂酰肌醇4，5-二磷酸（PIP 2）。我们确定了一个NaD 1：PIP 2复合物的晶体结构，揭示了一个惊人的低聚物的安排，包括七个二聚体的NaD 1，合作结合的阴离子头基的14个PIP 2分子通过一个独特的“阳离子抓地力”的配置。定点突变的NaD 1证实，PIP 2介导的寡聚化是重要的真菌和肿瘤细胞透化。这些观察结果确定了一个先天识别系统的NaD 1直接结合PIP 2，透化细胞通过一种新的膜破坏机制。DOI：http://dx.doi.org/10.7554/eLife.01808.001人们常说，攻击是最好的防御形式;植物和动物的免疫系统通常会瞄准微生物和其他病原体的细胞膜，以保护自己。破坏细胞膜会导致细胞中的基本内容物泄漏，最终细胞会破裂并死亡。大多数植物和动物产生一种叫做防御素的小蛋白质，通过攻击细胞膜来杀死微生物。这些防御素被认为要么通过覆盖其外表面来破坏细胞膜的稳定性，要么将它们插入膜中以形成开放的孔，从而允许重要的生物分子泄漏出细胞。然而，防御素攻击微生物膜的确切机制尚不清楚。在这项研究中，Poon、巴克斯特和Lay等人发现，一种名为NaD 1的防御素--它是从观赏烟草烟草中分离出来的--与细胞膜上一种名为磷脂酰肌醇4，5-二磷酸（简称PIP 2）的分子结合。Poon、巴克斯特、Lay等人通过计算出该复合物的三维结构，表明它含有14个弓形结构的PIP 2分子和14个NaD 1分子，并提出以这种方式螯合大量的PIP 2分子会使微生物的细胞膜不稳定。这些发现提出了一些问题：是否有其他小蛋白质可以以类似于防御素的方式破坏细胞膜的稳定性？其他生物的免疫系统是否也能识别微生物细胞膜上的分子，从而引发这种反击？此外，由于防御素也可以杀死肿瘤细胞，更好地了解它们的工作原理也可能导致人类癌症和其他疾病的新疗法。DOI：http://dx.doi.org/10.7554/eLife.01808.002网站
Cationic antimicrobial peptides (CAPs) such as defensins are ubiquitously found innate immune molecules that often exhibit broad activity against microbial pathogens and mammalian tumor cells. Many CAPs act at the plasma membrane of cells leading to membrane destabilization and permeabilization. In this study, we describe a novel cell lysis mechanism for fungal and tumor cells by the plant defensin NaD1 that acts via direct binding to the plasma membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2). We determined the crystal structure of a NaD1:PIP2 complex, revealing a striking oligomeric arrangement comprising seven dimers of NaD1 that cooperatively bind the anionic headgroups of 14 PIP2 molecules through a unique ‘cationic grip’ configuration. Site-directed mutagenesis of NaD1 confirms that PIP2-mediated oligomerization is important for fungal and tumor cell permeabilization. These observations identify an innate recognition system by NaD1 for direct binding of PIP2 that permeabilizes cells via a novel membrane disrupting mechanism. DOI: http://dx.doi.org/10.7554/eLife.01808.001 It is often said that attack is the best form of defense; and the immune systems of plants and animals will often target the cell membranes of microbes and other pathogens in order to defend themselves. Disrupting the cell membrane causes essential contents to leak from the cell, and eventually, the cell will burst and die. Most plants and animals produce small proteins called defensins that kill microbes by attacking their cell membranes. These defensins are thought to either destabilize the cell membrane by coating its outer surface or to insert themselves into the membrane to form open pores that allow vital biomolecules to leak out of the cell. However, the exact mechanism by which defensins attack microbial membranes is not understood. In this study, Poon, Baxter, Lay et al. show that a defensin called NaD1—which was isolated from the ornamental tobacco Nicotiana alata—binds to a molecule from the cell membrane called phosphatidylinositol 4,5-bisphosphate, or PIP2 for short. By working out the three-dimensional structure of this complex, Poon, Baxter, Lay et al. show that it contains 14 PIP2 molecules and 14 NaD1 molecules in an arch-shaped structure and suggest that sequestering large numbers of PIP2 molecules in this way destabilizes the cell membrane of the microbe. These findings raise a number of questions: are there other small proteins that can destabilize cell membranes in a similar manner to defensins? Do the immune systems of other organisms also recognize molecules from microbial cell membranes to trigger this kind of counterattack? Furthermore, since defensins can also kill tumor cells, a better understanding of how they work might also lead to new treatments for cancer and other diseases in humans. DOI: http://dx.doi.org/10.7554/eLife.01808.002