位于周質(zhì)空間的一種特殊蛋白DegP能幫助熱激和其他應(yīng)激下的大腸桿菌存活,。在常溫下( 25 °C)，DegP作為分子伴侶幫助其他蛋白的正確折疊,。而在高溫時(37–45 °C),，其卻作為蛋白酶高效降解未折疊或變性蛋白。清華大學(xué)隋森芳及其同事發(fā)現(xiàn)了,，DegP在蛋白質(zhì)控中如何調(diào)控它的雙重角色,。
之前的研究已經(jīng)顯示，DegP在與變性蛋白結(jié)合時形成籠形結(jié)構(gòu),。但DegP如何在其蛋白酶和分子伴侶功能的轉(zhuǎn)變卻未得以闡明,。
通過電子顯微鏡，隋森芳研究組發(fā)現(xiàn),，DegP在未結(jié)合底物的情況下,，能在類脂膜上形成碗形結(jié)構(gòu)低聚物（如圖）。該結(jié)構(gòu)同時顯示出分子伴侶和蛋白酶雙重活性,。
研究人員又測試了膜結(jié)合DegP與一系列未折疊蛋白的作用的情況,。結(jié)果顯示，在溶液中,，這種膜結(jié)合DegP碗形低聚物與非膜結(jié)合的DegP相比,，具有更高蛋白酶活性和更低分子伴侶活性,。這樣的發(fā)現(xiàn)提示，DegP蛋白通過在類脂膜上的聚集使其在兩種功能間轉(zhuǎn)換,。（生物谷Bioon.com）
生物谷推薦原始出處：
PNAS March 2, 2009, doi: 10.1073/pnas.0811780106
Bowl-shaped oligomeric structures on membranes as DegP's new functional forms in protein quality control
Qing-Tao Shena,1, Xiao-Chen Baia,1, Lei-Fu Changa, Yi Wub, Hong-Wei Wangc and Sen-Fang Suia,2
In the periplasm of Escherichia coli, DegP (also known as HtrA), which has both chaperone-like and proteolytic activities, prevents the accumulation of toxic misfolded and unfolded polypeptides. In solution, upon binding to denatured proteins, DegP forms large cage-like structures. Here, we show that DegP forms a range of bowl-shaped structures, independent of substrate proteins, each with a 4-, 5-, or 6-fold symmetry and all with a DegP trimer as the structural unit, on lipid membranes. These membrane-bound DegP assemblies have the capacity to recruit and process substrates in the bowl chamber, and they exhibit higher proteolytic and lower chaperone-like activities than DegP in solution. Our findings imply that DegP might regulate its dual roles during protein quality control, depending on its assembly state in the narrow bacterial envelope.
