近日，來自新加坡國立大學(xué)的研究者發(fā)現(xiàn)細(xì)菌可以對(duì)環(huán)境中的鹽分產(chǎn)生反應(yīng),，鹽分可以改變細(xì)菌特定鹽分效應(yīng)蛋白的行為,。這項(xiàng)新的研究發(fā)現(xiàn)揭示了微生物可以檢測水樣環(huán)境中的鹽分或者糖分水平,，相關(guān)研究已經(jīng)開展了超過30年,。相關(guān)研究成果刊登在了近日的國際雜志EMBO Journal上。
鹽分檢測蛋白類似發(fā)條
細(xì)菌可以產(chǎn)生感知環(huán)境改變并且對(duì)于改變做出效應(yīng)的機(jī)制,，比如環(huán)境中鹽分水平的改變,，有些細(xì)菌在低鹽分環(huán)境中生存，然而有些細(xì)菌在高鹽分環(huán)境中,，如腸道中生存,。運(yùn)用酰胺氫/氘交換質(zhì)譜法（HDXMS）,，研究者檢測了鹽分濃度的改變?nèi)绾伪皇荏w蛋白進(jìn)行感知。
研究者發(fā)現(xiàn)鹽分檢測蛋白就好像分子發(fā)條一樣,，這種蛋白可以從高濃度形式到展開形式進(jìn)行不斷地移位,，增加鹽分的濃度可以緩沖這種發(fā)條似的運(yùn)動(dòng)，進(jìn)而激活蛋白質(zhì)活性,，這種蛋白質(zhì)的運(yùn)動(dòng)方式提供了一種統(tǒng)一的模式來揭示細(xì)菌如何感知環(huán)境,。
識(shí)別不同蛋白質(zhì)如何以分子發(fā)條來進(jìn)行運(yùn)動(dòng)對(duì)于我們理解這些蛋白質(zhì)如何來工作至關(guān)重要，目前研究人員通過給這些細(xì)菌效應(yīng)蛋白質(zhì)包埋人工膜來研究蛋白質(zhì)的功能,，研究者希望理解這些膜是如何促成對(duì)蛋白質(zhì)活性,、結(jié)構(gòu)、穩(wěn)定性和對(duì)鹽分的效應(yīng)的作用的,。（生物谷Bioon.com）
編譯自：How Bacteria Sense Salt Stress
doi:10.1038/emboj.2012.99
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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.
