Hucke Oliver, Schiltz Emile, Drews Gerhart, Labahn Andreas
Institut für Physikalische Chemie, Albertstr. 23a, Universität Freiburg, D-79104 Freiburg, Germany.
FEBS Lett. 2003 Jan 30;535(1-3):166-70. doi: 10.1016/s0014-5793(02)03899-1.
Most of the bacterial photosynthetic reaction centres known to date contain a cytochrome subunit with four covalently bound haem groups. In the case of Blastochloris viridis, this reaction centre subunit is anchored in the membrane by a lipid molecule covalently attached to the cysteine which forms the N-terminus of the mature protein after processing by a signal peptidase. We show that posttranslational N-terminal cleavage of the cytochrome subunit does not occur in the aerobic photosynthetic bacterium Roseobacter denitrificans. From sequence analysis of the resulting elongated N-terminus it follows that a transmembrane helix is anchoring the reaction centre-bound cytochrome in the membrane. Comparative sequence analysis strongly suggests that all cytochrome subunits lacking the lipid coupling cysteine share this structural feature. Comparison of the N-terminal segment of the cytochrome subunit of Roseobacter denitrificans with the sequences of the PufX proteins from Rhodobacter sphaeroides and Rhodobacter capsulatus suggests a phylogenetic relation.
迄今为止已知的大多数细菌光合反应中心都包含一个细胞色素亚基，该亚基带有四个共价结合的血红素基团。就绿硫菌而言，这个反应中心亚基通过一个与半胱氨酸共价连接的脂质分子锚定在膜中，该半胱氨酸在信号肽酶加工后形成成熟蛋白的N端。我们发现，在好氧光合细菌反硝化红细菌中，细胞色素亚基不会发生翻译后N端切割。通过对所得延长N端的序列分析可知，一个跨膜螺旋将结合在反应中心的细胞色素锚定在膜中。比较序列分析强烈表明，所有缺乏脂质偶联半胱氨酸的细胞色素亚基都具有这一结构特征。将反硝化红细菌细胞色素亚基的N端片段与球形红细菌和荚膜红细菌的PufX蛋白序列进行比较，提示了一种系统发育关系。
