Lyska Dagmar, Paradies Susanne, Meierhoff Karin, Westhoff Peter
Institut für Entwicklungs- und Molekularbiologie der Pflanzen, Heinrich-Heine-Universität, Universitätsstrasse 1, Düsseldorf, Germany.
Plant Cell Physiol. 2007 Dec;48(12):1737-46. doi: 10.1093/pcp/pcm146. Epub 2007 Oct 29.
The cytochrome b(6) subunit of the cytochrome b(6)f complex is a multiheme protein. Two b-type hemes are bound non-covalently to the protein, whereas the third heme (heme c(n)) is covalently attached via an atypical thioether bond. To understand the maturation of cytochrome b(6) and to identify the assisting factors, we characterized the ethyl methanesulfonate-induced nuclear mutant hcf208. This Arabidopsis mutant shows a high chlorophyll fluorescence phenotype and does not accumulate the major cytochrome b(6)f complex subunits. Transcript levels and patterns of the four major polypeptides of the complex are equal to those of the wild type. The mutant cytochrome b(6) polypeptide shows a faster migration behavior in SDS-PAGE compared with the wild type and it has no peroxidase activity. The HCF208 locus was mapped and the gene was cloned. Sequence analysis revealed that HCF208 is a homolog of the Chlamydomonas reinhardtii CCB2 protein, which is a factor mediating attachment of heme c(n) to the cytochrome b(6) polypeptide as part of a novel heme biogenesis pathway, called system IV. Blue Native PAGE revealed residual amounts of the cytochrome b(6)f complex dimer in hcf208; however, this form is unable to participate in electron transport reactions.
细胞色素b6f复合体的细胞色素b6亚基是一种多血红素蛋白。两个b型血红素通过非共价键与该蛋白结合，而第三个血红素（血红素c(n)）则通过一个非典型硫醚键共价连接。为了了解细胞色素b6的成熟过程并鉴定辅助因子，我们对甲磺酸乙酯诱导的细胞核突变体hcf208进行了表征。这个拟南芥突变体表现出高叶绿素荧光表型，并且不积累细胞色素b6f复合体的主要亚基。该复合体四种主要多肽的转录水平和模式与野生型相同。与野生型相比，突变体细胞色素b6多肽在SDS-PAGE中迁移速度更快，并且没有过氧化物酶活性。对HCF208基因座进行了定位并克隆了该基因。序列分析表明，HCF208是莱茵衣藻CCB2蛋白的同源物，CCB2蛋白是一种作为新的血红素生物合成途径（称为系统IV）的一部分介导血红素c(n)与细胞色素b6多肽结合的因子。蓝色非变性聚丙烯酰胺凝胶电泳显示hcf208中存在残留量的细胞色素b6f复合体二聚体；然而，这种形式无法参与电子传递反应。
