A functional description of CymA, an electron-transfer hub supporting anaerobic respiratory flexibility in Shewanella
A functional description of CymA, an electron-transfer hub supporting anaerobic respiratory flexibility in Shewanella
复制标题
DOI：
10.1042/bj20120197
复制
发表时间：
2012-06-15
影响因子：
4.1
通讯作者：
Butt, Julea N.
中科院分区：
文献类型：
--
作者：
Marritt, Sophie J.;Lowe, Thomas G.;Butt, Julea N.
CymA(四氢细胞色素c)是喹酚脱氢酶NAPC/NIRT家族中的一员。对于Shewanellae的厌氧呼吸灵活性来说，Cyma是必不可少的，它将电子从Menaquinol转移到各种专用系统，用于还原末端电子受体，包括富马酸和Fe(III)的不溶性矿物。圆锥希瓦氏菌MR-1菌株CymA的光谱特征鉴定了三个低自旋的His/His配位的c-Hem和一个高自旋的c-Hem，其中His/H2O配位位于喹酚结合部位附近。在pH 7下，与2-庚基-4-羟基喹啉-N-氧化物结合不会改变高自旋(约240 mV)和低自旋(约110、190和265 mV)HEM的中点电势，这些中点电势似乎倾向于在喹酚氧化后将电子从高自旋中心转移到低自旋中心。在NADH(Em=320 mV)和2-甲基-1，4-萘二酮(2-甲基-1，4-萘醌)氧化还原酶的存在下，Cyma被甲二醇(E-m=80 mV)还原，而不是单独被甲二醇还原。在细胞质膜中，Cyma的还原可能需要NADH、甲酸盐或H-2氧化的热力学驱动力，因为分离的Menaquinol池的氧化还原平衡不足。光谱研究表明，CymA需要一个非血红素辅助因子来氧化喹酚，还原的酶与其氧化还原伙伴FCC(3)(富马酸黄色素c(3)还原酶)形成1：1的络合物。文中还讨论了Cyma对Shewanellae呼吸灵活性的支持作用。
CymA (tetrahaem cytochrome c) is a member of the NapC/NirT family of quinol dehydrogenases. Essential for the anaerobic respiratory flexibility of shewanellae, CymA transfers electrons from menaquinol to various dedicated systems for the reduction of terminal electron acceptors including fumarate and insoluble minerals of Fe(III). Spectroscopic characterization of CymA from Shewanella oneidensis strain MR-1 identifies three low-spin His/His co-ordinated c-haems and a single high-spin c-haem with His/H2O co-ordination lying adjacent to the quinol-binding site. At pH 7, binding of the menaquinol analogue, 2-heptyl-4-hydroxyquinoline-N-oxide, does not alter the midpoint potentials of the high-spin (approximately 240 mV) and low-spin (approximately 110, 190 and 265 mV) haems that appear biased to transfer electrons from the high- to low-spin centres following quinol oxidation. CymA is reduced with menadiol (E-m= 80 mV) in the presence of NADH (Em= 320 mV) and an NADH menadione (2-methyl-1,4-naphthoquinone) oxidoreductase, but not by menadiol alone. In cytoplasmic membranes reduction of CymA may then require the thermodynamic driving force from NADH, formate or H-2 oxidation as the redox poise of the menaquinol pool in isolation is insufficient. Spectroscopic studies suggest that CymA requires a non-haem co-factor for quinol oxidation and that the reduced enzyme forms a 1:1 complex with its redox partner Fcc(3) (flavocytochrome c(3) fumarate reductase). The implications for CymA supporting the respiratory flexibility of shewanellae are discussed.