Department of Molecular Biology and Microbiology, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4960, USA.
Mol Microbiol. 2010 Feb;75(4):924-41. doi: 10.1111/j.1365-2958.2009.07027.x.
Pseudomonas aeruginosa uses a type III secretion system to inject protein effectors into a targeted host cell. Effector secretion is triggered by host cell contact. How effector secretion is prevented prior to cell contact is not well understood. In all secretion systems studied to date, the needle tip protein is required for controlling effector secretion, but the mechanism by which needle tip proteins control effector secretion is unclear. Here we present data that the P. aeruginosa needle tip protein, PcrV, controls effector secretion by assembling into a functional needle tip complex. PcrV likely does not simply obstruct the secretion channel because the pore-forming translocator proteins can still be secreted while effector secretion is repressed. This finding suggests that PcrV controls effector secretion by affecting the conformation of the apparatus, shifting it from the default, effector secretion 'on' conformation, to the effector secretion 'off' conformation. We also present evidence that PcrG, which can bind to PcrV and is also involved in controlling effector export, is cytoplasmic and that the interaction between PcrG and PcrV is not required for effector secretion control by either protein. Taken together, these data allow us to propose a working model for control of effector secretion by PcrG and PcrV.
铜绿假单胞菌使用 III 型分泌系统将蛋白效应器注入靶宿主细胞。效应器的分泌是由宿主细胞接触触发的。在细胞接触之前，效应器分泌是如何被阻止的，目前还不是很清楚。在迄今为止研究的所有分泌系统中，针状尖端蛋白是控制效应器分泌所必需的，但针状尖端蛋白控制效应器分泌的机制尚不清楚。在这里，我们提供的数据表明，铜绿假单胞菌的针状尖端蛋白 PcrV 通过组装成一个功能性的针状尖端复合物来控制效应器的分泌。PcrV 可能不是简单地阻塞分泌通道，因为形成孔的转运蛋白仍然可以在效应物分泌被抑制的情况下被分泌。这一发现表明，PcrV 通过影响装置的构象来控制效应物的分泌，将其从默认的、效应物分泌“开启”构象转变为效应物分泌“关闭”构象。我们还提供了证据表明，与控制效应物输出有关的 PcrG 可以结合到 PcrV 上，并且它是细胞质的，而 PcrG 和 PcrV 之间的相互作用对于这两种蛋白质控制效应物分泌都是不需要的。总之，这些数据使我们能够提出一个由 PcrG 和 PcrV 控制效应物分泌的工作模型。
