Localization and Function of the Membrane-bound Riboflavin in the Na+-translocating NADH:Quinone Oxidoreductase (Na+-NQR) from Vibrio cholerae
Localization and Function of the Membrane-bound Riboflavin in the Na+-translocating NADH:Quinone Oxidoreductase (Na+-NQR) from Vibrio cholerae
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DOI：
10.1074/jbc.m109.071126
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发表时间：
2010-08-27
影响因子：
4.8
通讯作者：
Steuber, Julia
中科院分区：
文献类型：
--
作者：
Casutt, Marco S.;Huber, Tamara;Steuber, Julia
来自人类病原体霍乱弧菌的钠离子转运NADH：醌氧化还原酶（Na+-NQR）是一种呼吸膜蛋白复合物，其将NADH的氧化与Na+的跨膜转运偶联。Na+-NQR包括六个亚基NqrABCDEF，但这些亚基的化学计量和排列是未知的。氧化还原活性辅因子是FAD和NqrF上的2Fe-2S簇，NqrB和NqrC上共价连接的FMNs，以及复合物中定位未知的核黄素和泛醌-8。通过分析辅因子含量和NADH氧化活性的亚复合物的Na+-NQR缺乏个别的亚基，核黄素辅因子被明确地分配到膜结合的NqrB亚基。全复合物的N-末端氨基酸的定量分析显示，NqrB在全复合物中以单拷贝存在。它的结论是，疏水NqrB窝藏一个核黄素除了其共价连接的FMN。讨论了NqrB亚基中两种黄素在Na+-NQR还原泛醌生成泛醇过程中的催化作用。
The sodium ion-translocating NADH: quinone oxidoreductase (Na+-NQR) from the human pathogen Vibrio cholerae is a respiratory membrane protein complex that couples the oxidation of NADH to the transport of Na+ across the bacterial membrane. The Na+-NQR comprises the six subunits NqrABCDEF, but the stoichiometry and arrangement of these subunits are unknown. Redox-active cofactors are FAD and a 2Fe-2S cluster on NqrF, covalently attached FMNs on NqrB and NqrC, and riboflavin and ubiquinone-8 with unknown localization in the complex. By analyzing the cofactor content and NADH oxidation activity of subcomplexes of the Na+-NQR lacking individual subunits, the riboflavin cofactor was unequivocally assigned to the membrane-bound NqrB subunit. Quantitative analysis of the N-terminal amino acids of the holo-complex revealed that NqrB is present in a single copy in the holo-complex. It is concluded that the hydrophobic NqrB harbors one riboflavin in addition to its covalently attached FMN. The catalytic role of two flavins in subunit NqrB during the reduction of ubiquinone to ubiquinol by the Na+-NQR is discussed.