Huang Yafei, Reimann Joachim, Singh Laila M R, Adelroth Pia
Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden.
Biochim Biophys Acta. 2010 Jun-Jul;1797(6-7):724-31. doi: 10.1016/j.bbabio.2010.03.016. Epub 2010 Mar 20.
Heme-copper oxidases (HCuOs) are the terminal components of the respiratory chain in the mitochondrial membrane or the cell membrane in many bacteria. These enzymes reduce oxygen to water and use the free energy from this reaction to maintain a proton-motive force across the membrane in which they are embedded. The heme-copper oxidases of the cbb3-type are only found in bacteria, often pathogenic ones since they have a low Km for O2, enabling the bacteria to colonize semi-anoxic environments. Cbb3-type (C) oxidases are highly divergent from the mitochondrial-like aa3-type (A) oxidases, and within the heme-copper oxidase family, cbb3 is the closest relative to the most divergent member, the bacterial nitric oxide reductase (NOR). Nitric oxide reductases reduce NO to N2O without coupling the reaction to the generation of any electrochemical proton gradient. The significant structural differences between A- and C-type heme-copper oxidases are manifested in the lack in cbb3 of most of the amino acids found to be important for proton pumping in the A-type, as well as in the different binding characteristics of ligands such as CO, O2 and NO. Investigations of the reasons for these differences at a molecular level have provided insights into the mechanism of O2 and NO reduction as well as the proton-pumping mechanism in all heme-copper oxidases. In this paper, we discuss results from these studies with the focus on the relationship between proton transfer and ligand binding and reduction. In addition, we present new data, which show that CO binding to one of the c-type hemes of CcoP is modulated by protein-lipid interactions in the membrane. These results show that the heme c-CO binding can be used as a probe of protein-membrane interactions in cbb3 oxidases, and possible physiological consequences for this behavior are discussed.
血红素铜氧化酶（HCuOs）是线粒体膜或许多细菌细胞膜中呼吸链的末端成分。这些酶将氧气还原为水，并利用该反应产生的自由能来维持其嵌入膜中的质子动力势。cbb3型血红素铜氧化酶仅存在于细菌中，通常是病原菌，因为它们对氧气的米氏常数（Km）较低，使细菌能够在半缺氧环境中定殖。Cbb3型（C）氧化酶与线粒体样aa3型（A）氧化酶高度不同，在血红素铜氧化酶家族中，cbb3与最不同的成员——细菌一氧化氮还原酶（NOR）亲缘关系最近。一氧化氮还原酶将NO还原为N2O，而不将该反应与任何电化学质子梯度的产生相偶联。A-型和C-型血红素铜氧化酶之间显著的结构差异表现为，cbb3中缺乏大多数在A-型中对质子泵浦很重要的氨基酸，以及CO、O2和NO等配体的不同结合特性。在分子水平上对这些差异原因的研究为所有血红素铜氧化酶中O2和NO的还原机制以及质子泵浦机制提供了见解。在本文中，我们讨论这些研究的结果，重点是质子转移与配体结合和还原之间的关系。此外，我们还展示了新的数据，这些数据表明，CO与CcoP的一个c型血红素的结合受到膜中蛋白质-脂质相互作用的调节。这些结果表明，血红素c-CO结合可作为cbb3氧化酶中蛋白质-膜相互作用的探针，并讨论了这种行为可能产生的生理后果。
