細(xì)菌的“第六種分泌系統(tǒng)”(T6SS) 是負(fù)責(zé)將一系列毒性效應(yīng)物分子轉(zhuǎn)位到細(xì)菌和真核獵物細(xì)胞中去的一種細(xì)胞器,。這篇文章描述了來自PAAR-repeat超級家族的蛋白是怎樣在VgrG噬菌體尾尖（在穿透獵物細(xì)胞中所涉及的一種蛋白復(fù)合物）上形成一個(gè)尖的錐形延伸的，同時(shí)也描述了它們何以在吸收效應(yīng)物中也起一個(gè)作用,。這些數(shù)據(jù)支持關(guān)于T6SS的一個(gè)新模型：變細(xì)的尾尖被多種效應(yīng)物所裝飾，它們被一個(gè)由收縮驅(qū)動(dòng)的轉(zhuǎn)位事件一起輸送到目標(biāo)細(xì)胞內(nèi)。（生物谷Bioon.com）
生物谷推薦英文摘要：
Nature doi: 10.1038/nature12453
PAAR-repeat proteins sharpen and diversify the type VI secretion system spike
Mikhail M. Shneider, Sergey A. Buth,Brian T. Ho,Marek Basler, John J. Mekalanos & Petr G. Leiman
The bacterial type VI secretion system (T6SS) is a large multicomponent, dynamic macromolecular machine that has an important role in the ecology of many Gram-negative bacteria. T6SS is responsible for translocation of a wide range of toxic effector molecules, allowing predatory cells to kill both prokaryotic as well as eukaryotic prey cells1, 2, 3, 4, 5. The T6SS organelle is functionally analogous to contractile tails of bacteriophages and is thought to attack cells by initially penetrating them with a trimeric protein complex called the VgrG spike6, 7. Neither the exact protein composition of the T6SS organelle nor the mechanisms of effector selection and delivery are known. Here we report that proteins from the PAAR (proline-alanine-alanine-arginine) repeat superfamily form a sharp conical extension on the VgrG spike, which is further involved in attaching effector domains to the spike. The crystal structures of two PAAR-repeat proteins bound to VgrG-like partners show that these proteins sharpen the tip of the T6SS spike complex. We demonstrate that PAAR proteins are essential for T6SS-mediated secretion and target cell killing by Vibrio cholerae and Acinetobacter baylyi. Our results indicate a new model of the T6SS organelle in which the VgrG–PAAR spike complex is decorated with multiple effectors that are delivered simultaneously into target cells in a single contraction-driven translocation event.
