H+轉(zhuǎn)運(yùn)焦磷酸酶(H+-PPases)是活躍的質(zhì)子轉(zhuǎn)運(yùn)體,，它通過水解焦磷酸(PPi)建立了跨膜的質(zhì)子梯度。
H+-PPases以同源二聚體的形式首次發(fā)現(xiàn)于植物液泡膜,，以及幾種原生動物和原核生物的細(xì)胞膜。
到目前為止,，H+-PPases的三維結(jié)構(gòu)以及質(zhì)子轉(zhuǎn)運(yùn)的詳盡機(jī)制還未可知,。近日，由綠豆H+-PPase(VrH+-PPase)與亞氨二磷酸鹽(IDP,，一種非水解的底物類似物)形成的復(fù)合物由臺灣國立清華大學(xué)Yuh-Ju Sun教授等人所解析,，在2.35埃的分辨率。相關(guān)論文在線發(fā)表在3月28日的Nature,。
研究發(fā)現(xiàn),，每一個VrH+-PPase亞基都包含了一個由16個跨膜螺旋形成的完整的膜結(jié)構(gòu)域。IDP被結(jié)合到細(xì)胞質(zhì)基質(zhì)區(qū)域的每個亞基,，并被大量的帶電殘基和5個Mg2+捕獲,。
這個以前沒有描述的質(zhì)子轉(zhuǎn)運(yùn)通路由6個核心跨膜螺旋形成。質(zhì)子泵能夠被PPi的水解所起始,，H+然后通過一個由Arg242, Asp294, Lys742及Glu301組成的通路被轉(zhuǎn)運(yùn)進(jìn)液泡腔,，。
研究人員因此建立一個偶聯(lián)質(zhì)子泵以及PPi的水解的工作模型,。（生物谷Deepblue編譯）
doi: 10.1038/nature10963
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Crystal structure of a membrane-embedded H+-translocating pyrophosphatase
Shih-Ming Lin, Jia-Yin Tsai, Chwan-Deng Hsiao, Yun-Tzu Huang, Chen-Liang Chiu,Mu-Hsuan Liu, Jung-Yu Tung, Tseng-Huang Liu, Rong-Long Pan & Yuh-Ju Sun.
H+-translocating pyrophosphatases (H+-PPases) are active proton transporters that establish a proton gradient across the endomembrane by means of pyrophosphate (PPi) hydrolysis.H+-PPases are found primarily as homodimers in the vacuolar membrane of plants and the plasma membrane of several protozoa and prokaryotes.The three-dimensional structure and detailed mechanisms underlying the enzymatic and proton translocation reactions of H+-PPases are unclear. Here we report the crystal structure of a Vigna radiata H+-PPase (VrH+-PPase) in complex with a non-hydrolysable substrate analogue, imidodiphosphate (IDP), at 2.35? resolution.Each VrH+-PPase subunit consists of an integral membrane domain formed by 16 transmembrane helices. IDP is bound in the cytosolic region of each subunit and trapped by numerous charged residues and five Mg2+ ions.A previously undescribed proton translocation pathway is formed by six core transmembrane helices. Proton pumping can be initialized by PPi hydrolysis, and H+ is then transported into the vacuolar lumen through a pathway consisting of Arg242, Asp294, Lys742 and Glu301.We propose a working model of the mechanism for the coupling between proton pumping and PPi hydrolysis by H+-PPases
