Center for Infectious Disease Research, Medical College of Wisconsin Milwaukee, WI, USA.
Front Microbiol. 2011 Jul 4;2:142. doi: 10.3389/fmicb.2011.00142. eCollection 2011.
Pseudomonas aeruginosa possesses a type III secretion system (T3SS) to intoxicate host cells and evade innate immunity. This virulence-related machinery consists of a molecular syringe and needle assembled on the bacterial surface, which allows delivery of T3 effector proteins into infected cells. To accomplish a one-step effector translocation, a tip protein is required at the top end of the T3 needle structure. Strains lacking expression of the functional tip protein fail to intoxicate host cells. P. aeruginosa encodes a T3S that is highly homologous to the proteins encoded by Yersinia spp. The needle-tip proteins of Yersinia, LcrV, and P. aeruginosa, PcrV, share 37% identity and 65% similarity. Other known tip proteins are AcrV (Aeromonas), IpaD (Shigella), SipD (Salmonella), BipD (Burkholderia), EspA (EPEC, EHEC), Bsp22 (Bordetella), with additional proteins identified from various Gram-negative species, such as Vibrio and Bordetella. The tip proteins can serve as a protective antigen or may be critical for sensing host cells and evading innate immune responses. Recognition of the host microenvironment transcriptionally activates synthesis of T3SS components. The machinery appears to be mechanically controlled by the assemblage of specific junctions within the apparatus. These junctions include the tip and base of the T3 apparatus, the needle proteins and components within the bacterial cytoplasm. The tip proteins likely have chaperone functions for translocon proteins, allowing the proper assembly of translocation channels in the host membrane and completing vectorial delivery of effector proteins into the host cytoplasm. Multi-functional features of the needle-tip proteins appear to be intricately controlled. In this review, we highlight the functional aspects and complex controls of T3 needle-tip proteins with particular emphasis on PcrV and LcrV.
铜绿假单胞菌拥有 III 型分泌系统（T3SS）来毒害宿主细胞并逃避先天免疫。这种与毒力相关的机制由组装在细菌表面上的分子注射器和针组成，允许将 T3 效应蛋白递送到感染细胞中。为了完成一步效应物易位，需要在 T3 针结构的顶端有一个尖端蛋白。缺乏功能性尖端蛋白表达的菌株无法毒害宿主细胞。铜绿假单胞菌编码的 T3S 与耶尔森氏菌属编码的蛋白高度同源。耶尔森氏菌的针尖端蛋白 LcrV 和铜绿假单胞菌的 PcrV 共享 37%的同一性和 65%的相似性。其他已知的尖端蛋白是 Aeromonas 的 AcrV、Shigella 的 IpaD、Salmonella 的 SipD、Burkholderia 的 BipD、EPEC、EHEC 的 EspA、Bordetella 的 Bsp22，还有其他一些来自各种革兰氏阴性物种的蛋白，如弧菌和博德特氏菌。尖端蛋白可以作为保护性抗原，也可能对感知宿主细胞和逃避先天免疫反应至关重要。宿主微环境的识别转录激活 T3SS 成分的合成。该机制似乎通过在装置内组装特定的连接点来机械控制。这些连接点包括 T3 装置的尖端和底部、针蛋白和细菌细胞质内的成分。尖端蛋白可能对转位蛋白具有伴侣功能，允许在宿主膜中正确组装转位通道，并将效应蛋白有效地递送到宿主细胞质中。针尖端蛋白的多功能特性似乎受到复杂的控制。在这篇综述中，我们强调了 T3 针尖端蛋白的功能方面和复杂控制，特别强调了 PcrV 和 LcrV。
