H+转运焦磷酸酶(H+-PPases)是活跃的质子转运体,它通过水解焦磷酸(PPi)建立了跨膜的质子梯度。
H+-PPases以同源二聚体的形式首次发现于植物液泡膜,以及几种原生动物和原核生物的细胞膜。
到目前为止,H+-PPases的三维结构以及质子转运的详尽机制还未可知。近日,由绿豆H+-PPase(VrH+-PPase)与亚氨二磷酸盐(IDP,一种非水解的底物类似物)形成的复合物由台湾国立清华大学Yuh-Ju Sun教授等人所解析,在2.35埃的分辨率。相关论文在线发表在3月28日的Nature。
研究发现,每一个VrH+-PPase亚基都包含了一个由16个跨膜螺旋形成的完整的膜结构域。IDP被结合到细胞质基质区域的每个亚基,并被大量的带电残基和5个Mg2+捕获。
这个以前没有描述的质子转运通路由6个核心跨膜螺旋形成。质子泵能够被PPi的水解所起始,H+然后通过一个由Arg242, Asp294, Lys742及Glu301组成的通路被转运进液泡腔,。
研究人员因此建立一个偶联质子泵以及PPi的水解的工作模型。(生物谷Deepblue编译)
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