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首页> 外文期刊>Journal of Molecular Biology >Structure of the Cytochrome b(6)f Complex: Quinone Analogue Inhibitors as Ligands of Heme c(n).
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Structure of the Cytochrome b(6)f Complex: Quinone Analogue Inhibitors as Ligands of Heme c(n).

机译：细胞色素b（6）f配合物的结构：醌类抑制剂作为血红素c（n）的配体。

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A native structure of the cytochrome b(6)f complex with improved resolution was obtained from crystals of the complex grown in the presence of divalent cadmium. Two Cd(2+) binding sites with different occupancy were determined: (i) a higher affinity site, Cd1, which bridges His143 of cytochrome f and the acidic residue, Glu75, of cyt b(6); in addition, Cd1 is coordinated by 1-2 H(2)O or 1-2 Cl(-); (ii) a second site, Cd2, of lower affinity for which three identified ligands are Asp58 (subunit IV), Glu3 (PetG subunit) and Glu4 (PetM subunit). Binding sites of quinone analogue inhibitors were sought to map the pathway of transfer of the lipophilic quinone across the b(6)f complex and to define the function of the novel heme c(n). Two sites were found for the chromone ring of the tridecyl-stigmatellin (TDS) quinone analogue inhibitor, one near the p-side [2Fe-2S] cluster. A second TDS site was found on the n-side of the complex facing the quinone exchange cavity as an axial ligand of heme c(n). A similar binding site proximal to heme c(n) was found for the n-side inhibitor, NQNO. Binding of these inhibitors required their addition to the complex before lipid used to facilitate crystallization. The similar binding of NQNO and TDS as axial ligands to heme c(n) implies that this heme utilizes plastoquinone as a natural ligand, thus defining an electron transfer complex consisting of hemes b(n), c(n), and PQ, and the pathway of n-side reduction of the PQ pool. The NQNO binding site explains several effects associated with its inhibitory action: the negative shift in heme c(n) midpoint potential, the increased amplitude of light-induced heme b(n) reduction, and an altered EPR spectrum attributed to interaction between hemes c(n) and b(n). A decreased extent of heme c(n) reduction by reduced ferredoxin in the presence of NQNO allows observation of the heme c(n) Soret band in a chemical difference spectrum.
机译：从在二价镉存在下生长的复合物的晶体获得具有改善的分辨率的细胞色素b（6）f复合物的天然结构。确定了两个具有不同占有率的Cd（2+）结合位点：（i）较高的亲和力位点Cd1，它桥接细胞色素f的His143和cyt b（6）的酸性残基Glu75;另外，Cd1由1-2 H（2）O或1-2 Cl（-）配位; （ii）具有较低亲和力的第二个位点Cd2，三个已鉴定的配体是Asp58（IV亚基），Glu3（PetG亚基）和Glu4（PetM亚基）。寻求醌类似物抑制剂的结合位点，以绘制亲脂性醌穿过b（6）f复合物的转移途径，并定义新型血红素c（n）的功能。发现了十三烷基-柱头蛋白（TDS）醌类似物抑制剂的色酮环的两个位点，一个靠近p侧[2Fe-2S]簇。在面向醌交换腔的复合物的n侧发现了第二个TDS位点，作为血红素c（n）的轴向配体。对于n-侧抑制剂NQNO，发现了与血红素c（n）近端相似的结合位点。这些抑制剂的结合需要在将脂质用于促进结晶之前将它们添加到复合物中。 NQNO和TDS作为轴向配体与血红素c（n）的相似结合意味着该血红素利用质体醌作为天然配体，从而定义了由血红素b（n），c（n）和PQ组成的电子转移复合物，并且PQ池n侧减少的途径。 NQNO结合位点解释了与其抑制作用相关的几种作用：血红素c（n）中点电位的负移，光诱导血红素b（n）还原的幅度增加以及归因于血红素c相互作用的EPR谱改变（n）和b（n）。在NQNO存在下，还原铁氧还蛋白降低的血红素c（n）还原程度，可以观察到化学差异谱中的血红素c（n）Soret带。

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