Riistama S, Hummer G, Puustinen A, Dyer R B, Woodruff W H, Wikström M
Helsinki Bioenergetics Group, Department of Medical Chemistry, Institute of Biomedical Sciences, and Biocentrum Helsinki, University of Helsinki, Finland.
FEBS Lett. 1997 Sep 8;414(2):275-80. doi: 10.1016/s0014-5793(97)01003-x.
We address the molecular mechanism by which the haem-copper oxidases translocate protons. Reduction of O2 to water takes place at a haem iron-copper (CuB) centre, and protons enter from one side of the membrane through a 'channel' structure in the enzyme. Statistical-mechanical calculations predict bound water molecules within this channel, and mutagenesis experiments show that breaking this water structure impedes proton translocation. Hydrogen-bonded water molecules connect the channel further via a conserved glutamic acid residue to a histidine ligand of CuB. The glutamic acid side chain may have to move during proton transfer because proton translocation is abolished if it is forced to interact with a nearby lysine or arginine. Perturbing the CuB ligand structure shifts an infrared mode that may be ascribed to the O-H stretch of bound water. This is sensitive to mutations of the glutamic acid, supporting its connectivity to the histidine. These results suggest key roles of bound water, the glutamic acid and the histidine copper ligand in the mechanism of proton translocation.
我们研究了血红素-铜氧化酶转运质子的分子机制。氧气还原为水发生在血红素铁-铜（CuB）中心，质子从膜的一侧通过酶中的“通道”结构进入。统计力学计算预测该通道内存在结合水分子，诱变实验表明破坏这种水结构会阻碍质子转运。氢键连接的水分子通过一个保守的谷氨酸残基将通道进一步连接到CuB的组氨酸配体。在质子转移过程中，谷氨酸侧链可能必须移动，因为如果它被迫与附近的赖氨酸或精氨酸相互作用，质子转运就会被消除。扰动CuB配体结构会使一种红外模式发生位移，该模式可能归因于结合水的O-H伸缩振动。这对谷氨酸的突变很敏感，支持了它与组氨酸的连接。这些结果表明结合水、谷氨酸和组氨酸铜配体在质子转运机制中起关键作用。
