Structure of the cytochrome b6f complex:: new prosthetic groups, Q-space, and the "hors d'oeuvres hypothesis" for assembly of the complex
Structure of the cytochrome b6f complex:: new prosthetic groups, Q-space, and the "hors d'oeuvres hypothesis" for assembly of the complex
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DOI：
10.1007/s11120-004-2149-5
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发表时间：
2005-07-01
影响因子：
3.7
通讯作者：
Smith, JL
中科院分区：
文献类型：
--
作者：
Cramer, WA;Yan, JS;Smith, JL
细胞色素b(6)f复合体的3埃晶体结构为光合作用电子传递链提供了结构框架。本文报道了嗜热蓝藻Mastigocladis laminosus(Kurisu et al.)的22万分子量二聚体细胞色素b(6)f的结构。2003，Science 302：1009-1014)和绿藻，莱茵衣藻(Stroebel et al.2003年，自然426：413 418)，非常相似。后者是来自真核生物来源的完整膜光合电子传递复合体的第一个结构。Laminosus和C.reinhardtii的结构为三个天然和新的假体基团的性质和功能提供了结构信息和实验见解，这三个基团是一个叶绿素a，一个β-胡萝卜素和一个独特的血红素x，在细胞色素b(6)f复合体的每个单体中都有一个拷贝，但在动物和酵母线粒体呼吸链的细胞色素BC(1)复合体中没有。从这些结构中已经获得了一些功能上的见解，包括二聚体的功能；血红素x的性质；单体间醌交换空腔的功能；通过相对狭窄的缝隙或门户的醌扩散途径；改进的n侧醌氧化还原反应的反应方案；结合的叶绿素a猝灭结合的叶绿素三线态的必然新的机制；结合的叶绿素a在LHC激酶激活中的可能作用；以及PETG、L、M和N四个小亚单位的结构和组装作用。根据疏水小亚基的顺式正取向和β-胡萝卜素的牙签结合模式，提出了复合体外围的疏水小棒或尖桩栅栏多肽的组装“开胃菜假说”。
3-angstrom crystal structures of the cytochrome b(6) f complex have provided a structural framework for the photosynthetic electron transport chain. The structures of the 220,000 molecular weight dimeric cytochrome b(6) f complex from the thermophilic cyanobacterium, Mastigocladis laminosus (Kurisu et al. 2003, Science 302: 1009 - 1014), and the green alga, Chlamydomonas reinhardtii (Stroebel et al. 2003, Nature 426: 413 418), are very similar. The latter is the first structure of a integral membrane photosynthetic electron transport complex from a eukaryotic source. The M. laminosus and C. reinhardtii structures have provided structural information and experimental insights to the properties and functions of three native and novel prosthetic groups, a chlorophyll a, a beta-carotene, and a unique heme x, one copy of which is found in each monomer of the cytochrome b(6) f complex, but not the cytochrome bc(1) complex from the mitochondrial respiratory chain of animals and yeast. Several functional insights have emerged from the structures including the function of the dimer; the properties of heme x; the function of the inter-monomer quinone-exchange cavity; a quinone diffusion pathway through relatively narrow crevices or portals; a modified reaction scheme for n-side quinone redox reactions; a necessarily novel mechanism for quenching of the bound chlorophyll triplet state; a possible role for the bound chlorophyll a in activation of the LHC kinase; and a structural and assembly role for the four small PetG, L, M, and N subunits. An 'hors d'oeuvres hypothesis' for assembly of the complex is proposed for the small 'hydrophobic stick' or 'picket fence' polypeptides at the periphery of the complex, based on the cis-positive orientation of the small hydrophobic subunits and the 'toothpick' binding mode of the beta-carotene.