The evolutionary origin of the protein-translocating channel of chloroplastic envelope membranes: Identification of a cyanobacterial homolog
The evolutionary origin of the protein-translocating channel of chloroplastic envelope membranes: Identification of a cyanobacterial homolog
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DOI：
10.1073/pnas.96.2.784
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发表时间：
1999-01-19
影响因子：
11.1
通讯作者：
Keegstra, K
中科院分区：
文献类型：
--
作者：
Reumann, S;Davila-Aponte, J;Keegstra, K
已知的叶绿体蛋白输入装置的包膜蛋白与其他真核或原核蛋白转运系统的蛋白缺乏序列相似性。然而，我们在蓝藻聚胞菌（synnechocystis sp, PCC 6803）的基因组中发现了一个推测的同源基因，该基因编码豌豆叶绿体外包膜蛋白易位通道Toc75，我们研究了21%的低序列同源性是否反映了两种蛋白之间的结构和功能关系。我们提供的证据表明，蓝藻蛋白也定位于外膜。根据这些信息和预测二级结构的相似性，我们得出结论，Toc75与蓝藻蛋白（SynToc75）是结构同源的，SynToc75是必不可少的，因为在定向诱变后没有恢复纯合的零突变体，序列分析表明SynToc75属于一个功能尚不清楚的cramm阴性细菌外膜蛋白家族。然而，我们证明这些蛋白质与一组特定的原核分泌通道有关，这些通道将毒力因子（如溶血素和粘附素）转移到外膜上。
The known envelope membrane proteins of the chloroplastic protein import apparatus lack sequence similarity to proteins of other eukaryotic or prokaryotic protein transport systems. However, we detected a putative homolog of the gene encoding Toc75, the protein-translocating channel from the outer envelope membrane of pea chloroplasts, in the genome of the cyanobacterium Synechocystis sp, PCC 6803, We investigated whether the low sequence identity of 21% reflects a structural and functional relationship between the two proteins. We provide evidence that the cyanobacterial protein is also localized in the outer membrane. From this information and the similarity of the predicted secondary structures, we conclude that Toc75 and the cyanobacterial protein, referred to as SynToc75, are structural homologs, synToc75 is essential, as homozygous null mutants were not recovered after directed mutagenesis, Sequence analysis indicates that SynToc75 belongs to a family of outer membrane proteins from Cram-negative bacteria whose function is not yet known. However, we demonstrate that these proteins are related to a specific group of prokaryotic secretion channels that transfer virulence factors, such as hemolysins and adhesins, across the outer membrane.