McDonald Christopher, Jovanovic Goran, Ces Oscar, Buck Martin
Department of Chemistry, Imperial College London, London, United Kingdom Institute of Chemical Biology, Imperial College London, London, United Kingdom.
Department of Life Sciences, Imperial College London, London, United Kingdom.
mBio. 2015 Sep 1;6(5):e01188-15. doi: 10.1128/mBio.01188-15.
Phage shock protein A (PspA), which is responsible for maintaining inner membrane integrity under stress in enterobacteria, and vesicle-inducting protein in plastids 1 (Vipp1), which functions for membrane maintenance and thylakoid biogenesis in cyanobacteria and plants, are similar peripheral membrane-binding proteins. Their homologous N-terminal amphipathic helices are required for membrane binding; however, the membrane features recognized and required for expressing their functionalities have remained largely uncharacterized. Rigorously controlled, in vitro methodologies with lipid vesicles and purified proteins were used in this study and provided the first biochemical and biophysical characterizations of membrane binding by PspA and Vipp1. Both proteins are found to sense stored curvature elastic (SCE) stress and anionic lipids within the membrane. PspA has an enhanced sensitivity for SCE stress and a higher affinity for the membrane than Vipp1. These variations in binding may be crucial for some of the proteins' differing roles in vivo. Assays probing the transcriptional regulatory function of PspA in the presence of vesicles showed that a relief of transcription inhibition occurs in an SCE stress-specific manner. This in vitro recapitulation of membrane stress-dependent transcription control suggests that the Psp response may be mounted in vivo when a cell's inner membrane experiences increased SCE stress.
All cell types maintain the integrity of their membrane systems. One widely distributed membrane stress response system in bacteria is the phage shock protein (Psp) system. The central component, peripheral membrane protein PspA, which mitigates inner membrane stress in bacteria, has a counterpart, Vipp1, which functions for membrane maintenance and thylakoid biogenesis in plants and photosynthetic bacteria. Membrane association of both these proteins is accepted as playing a pivotal role in their functions. Here we show that direct membrane binding by PspA and Vipp1 is driven by two physio-chemical signals, one of which is membrane stress specific. Our work points to alleviation of membrane stored curvature elastic stress by amphipathic helix insertions as an attractive mechanism for membrane maintenance by PspA and Vipp1. Furthermore, the identification of a physical, stress-related membrane signal suggests a unilateral mechanism that promotes both binding of PspA and induction of the Psp response.
噬菌体休克蛋白A（PspA）负责在肠道细菌受到压力时维持内膜完整性，而质体中的囊泡诱导蛋白1（Vipp1）在蓝细菌和植物中负责膜维持和类囊体生物合成，它们是相似的外周膜结合蛋白。它们同源的N端两亲性螺旋是膜结合所必需的；然而，表达其功能所识别和需要的膜特征在很大程度上仍未得到表征。本研究采用了对脂质囊泡和纯化蛋白进行严格控制的体外方法，首次对PspA和Vipp1的膜结合进行了生化和生物物理表征。发现这两种蛋白都能感知膜内储存的曲率弹性（SCE）应力和阴离子脂质。PspA对SCE应力的敏感性增强，对膜的亲和力高于Vipp1。这些结合上的差异可能对这些蛋白在体内的不同作用至关重要。在囊泡存在的情况下探测PspA转录调控功能的实验表明，转录抑制的缓解以SCE应激特异性方式发生。这种膜应激依赖性转录控制的体外重现表明，当细胞内膜经历增加的SCE应激时，Psp反应可能在体内发生。
所有细胞类型都维持其膜系统的完整性。细菌中一种广泛分布的膜应激反应系统是噬菌体休克蛋白（Psp）系统。核心成分外周膜蛋白PspA可减轻细菌内膜应激，它在植物和光合细菌中有一个对应物Vipp1，其功能是膜维持和类囊体生物合成。这两种蛋白与膜的结合被认为在其功能中起关键作用。在这里，我们表明PspA和Vipp1与膜的直接结合由两种物理化学信号驱动，其中一种是膜应激特异性的。我们的工作指出，两亲性螺旋插入减轻膜储存的曲率弹性应力是PspA和Vipp1维持膜的一种有吸引力的机制。此外，对一种与应激相关的物理膜信号的鉴定表明了一种促进PspA结合和Psp反应诱导的单向机制。
