The Q cycle of cytochrome bc complexes: a structure perspective.
The Q cycle of cytochrome bc complexes: a structure perspective.
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DOI：
10.1016/j.bbabio.2011.02.006
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发表时间：
2011-07
影响因子：
4.3
通讯作者：
Yamashita, Eiki
中科院分区：
文献类型：
--
作者：
Cramer, William A.;Hasan, S. Saif;Yamashita, Eiki
关键词：
异源寡聚细胞色素bc 1和b6 f（“bc”）的晶体结构的方面有关的电子/质子转移功能和相关的氧化还原反应的亲脂性醌类化合物进行了讨论。强调了b6 f和bc 1复合物之间的差异。细胞色素bc 1和b6 f二聚体复合物在结构上从配位氧化还原基团的亚基核心发散，所述亚基核心由两个双组氨酸配位的血红素组成，在复合物的电化学负（n）侧和正（p）侧的血红素bn和bp，分别在p侧水界面和水相的高电位[2Fe-2S]簇和c型血红素，以及复合物的n-和p-侧上的醌/醌醇结合位点。bc 1和b6 f复合体在亚基组成和结构上偏离了这个核心。B6 F还含有另外的辅基，包括N侧的C型血红素CN和叶绿素α和β-胡萝卜素。对称二聚体的常见结构和功能。(I)醌与双分子层交换。bc 1和b6 f复合物共有一个单体间无蛋白质空腔，其长度约为30沿着膜法线× 25（中心单体间距离）× 15（中心深度），提供了一个小生境，其中亲脂性醌/醌醇（Q/QH 2）可以与膜双层交换。(II)电子转移。的二聚体结构和接近的两个血红素bp的电化学正侧的复合物中的两个单体单元允许两个替代路线的电子转移跨越复合物从血红素bp到bn的可能性：单体内，和单体间涉及电子交叉之间的两个血红素bp。一个基于结构的总结血红素间的距离在7个公元前复合物，线粒体，色素细胞，蓝藻，藻类来源，表明，基于距离参数，单体内的途径将有利于动力学。(III)醌结合位点的分离。二聚体结构和Q/QH 2结合位点的位置的结果是p侧QH 2氧化和n侧Q还原位点各自很好地分离。因此，在QH 2或Q分子在两个氧化或还原位点的停留时间重叠的情况下，它们的空间分离将导致延伸的Q或QH 2类异戊二烯链之间的空间干扰最小。(IV)跨膜QH 2/Q转移。(i)n/p侧QH 2/Q转移可能受到脂质酰基链的阻碍;（ii）跨越复合物的较短的较少阻碍的单体间途径不会穿过空腔的中心，这是从一个单体上的n侧抗霉素位点和另一个单体上的p侧豆磷蛋白位点推断的，所述位点位于复合物的同一表面上。(V)用于QH 2/Q通道的窄p侧入口。作为氧化剂的[2Fe-2S]簇，其组氨酸配体在QH 2的氧化中作为H+受体，通过狭窄的扩展门户连接到单体间空腔，该门户也被结合叶绿素的20个碳植基链占据在b6 f复合物中。
Aspects of the crystal structures of the hetero-oligomeric cytochrome bc1 and b6f (“bc”) complexes relevant to their electron/proton transfer function and the associated redox reactions of the lipophilic quinones are discussed. Differences between the b6f and bc1 complexes are emphasized. The cytochrome bc1 and b6f dimeric complexes diverge in structure from a core of subunits that coordinate redox groups consisting of two bis-histidine coordinated hemes, a heme bn and bp on the electrochemically negative (n) and positive (p) sides of the complex, the high potential [2Fe-2S] cluster and c-type heme at the p-side aqueous interface and aqueous phase, respectively, and quinone/quinol binding sites on the n- and p-sides of the complex. The bc1 and b6f complexes diverge in subunit composition and structure away from this core. b6f also contains additional prosthetic groups including a c-type heme cn on the n-side, and a chlorophyll a and β-carotene. Common structure aspects; functions of the symmetric dimer. (I) Quinone exchange with the bilayer. An inter-monomer protein-free cavity of approximately 30 Å along the membrane normal × 25 Å (central inter-monomer distance) × 15 Å (depth in the center), is common to both bc1 and b6f complexes, providing a niche in which the lipophilic quinone/quinol (Q/QH2) can be exchanged with the membrane bilayer. (II) Electron transfer. The dimeric structure and the proximity of the two hemes bp on the electrochemically positive side of the complex in the two monomer units allow the possibility of two alternate routes of electron transfer across the complex from heme bp to bn,: intra-monomer, and inter-monomer involving electron cross-over between the two hemes bp. A structure-based summary of inter-heme distances in seven bc complexes, representing mitochondrial, chromatophore, cyanobacterial, and algal sources, indicates that, based on the distance parameter, the intra-monomer pathway would be favored kinetically. (III) Separation of quinone binding sites. A consequence of the dimer structure and the position of the Q/QH2binding sites is that the p-side QH2 oxidation and n-side Q reduction sites are each well separated. Therefore, In the event of an overlap in residence time by QH2 or Q molecules at the two oxidation or reduction sites, their spatial separation would result in minimal steric interference between extended Q or QH2 isoprenoid chains. (IV) Trans-membrane QH2/Q transfer. (i) n/p side QH2/Q transfer may be hindered by lipid acyl chains; (ii) the shorter less hindered inter-monomer pathway across the complex would not pass through the center of the cavity, as inferred from the n-side antimycin site on one monomer and the p-side stigmatellin site on the other residing on the same surface of the complex. (V) Narrow p-Side portal for QH2/Q passage. The [2Fe-2S] cluster that serves as oxidant, and whose hisitidine ligand serves as a H+ acceptor in the oxidation of QH2, is connected to the inter-monomer cavity by a narrow extended portal, which is also occupied in the b6f complex by the 20 carbon phytyl chain of the bound chlorophyll.
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影响因子：
5.6
作者：
Bönisch, H;Schmidt, CL;Ladenstein, R
通讯作者：
Ladenstein, R
影响因子：
5.6
作者：
BERRY, EA;HUANG, LS;JAP, BK
通讯作者：
JAP, BK
影响因子：
4.8
作者：
Breyton, C
通讯作者：
Breyton, C
影响因子：
4.4
作者：
BERATAN, DN;ONUCHIC, JN;HOPFIELD, JJ
通讯作者：
HOPFIELD, JJ
DOI：
10.1098/rstb.2002.1184
发表时间：
2003-01-29
期刊：
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY OF LONDON SERIES B-BIOLOGICAL SCIENCES
影响因子：
--
作者：
Baymann, F;Lebrun, E;Nitschke, W
通讯作者：
Nitschke, W