近日，来自新加坡国立大学的研究者发现细菌可以对环境中的盐分产生反应，盐分可以改变细菌特定盐分效应蛋白的行为。这项新的研究发现揭示了微生物可以检测水样环境中的盐分或者糖分水平，相关研究已经开展了超过30年。相关研究成果刊登在了近日的国际杂志EMBO Journal上。
盐分检测蛋白类似发条
细菌可以产生感知环境改变并且对于改变做出效应的机制，比如环境中盐分水平的改变，有些细菌在低盐分环境中生存，然而有些细菌在高盐分环境中，如肠道中生存。运用酰胺氢/氘交换质谱法（HDXMS），研究者检测了盐分浓度的改变如何被受体蛋白进行感知。
研究者发现盐分检测蛋白就好像分子发条一样，这种蛋白可以从高浓度形式到展开形式进行不断地移位，增加盐分的浓度可以缓冲这种发条似的运动，进而激活蛋白质活性，这种蛋白质的运动方式提供了一种统一的模式来揭示细菌如何感知环境。
识别不同蛋白质如何以分子发条来进行运动对于我们理解这些蛋白质如何来工作至关重要，目前研究人员通过给这些细菌效应蛋白质包埋人工膜来研究蛋白质的功能，研究者希望理解这些膜是如何促成对蛋白质活性、结构、稳定性和对盐分的效应的作用的。（生物谷Bioon.com）
编译自：How Bacteria Sense Salt Stress
doi:10.1038/emboj.2012.99
PMC:
PMID:
The inner membrane histidine kinase EnvZ senses osmolality via helix-coil transitions in the cytoplasm
Loo Chien Wang, Leslie K Morgan, Pahan Godakumbura, Linda J Kenney and Ganesh S Anand
Two-component systems mediate bacterial signal transduction, employing a membrane sensor kinase and a cytoplasmic response regulator (RR). Environmental sensing is typically coupled to gene regulation. Understanding how input stimuli activate kinase autophosphorylation remains obscure. The EnvZ/OmpR system regulates expression of outer membrane proteins in response to osmotic stress. To identify EnvZ conformational changes associated with osmosensing, we used HDXMS to probe the effects of osmolytes (NaCl, sucrose) on the cytoplasmic domain of EnvZ (EnvZc). Increasing osmolality decreased deuterium exchange localized to the four-helix bundle containing the autophosphorylation site (His243). EnvZc exists as an ensemble of multiple conformations and osmolytes favoured increased helicity. High osmolality increased autophosphorylation of His243, suggesting that these two events are linked. In-vivo analysis showed that the cytoplasmic domain of EnvZ was sufficient for osmosensing, transmembrane domains were not required. Our results challenge existing claims of robustness in EnvZ/OmpR and support a model where osmolytes promote intrahelical H-bonding enhancing helix stabilization, increasing autophosphorylation and downstream signalling. The model provides a conserved mechanism for signalling proteins that respond to diverse physical and mechanical stimuli.
