Trachtenberg Shlomo, Cohen-Krausz Sara
Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.
J Mol Microbiol Biotechnol. 2006;11(3-5):208-20. doi: 10.1159/000094055.
Common prokaryotic motility modes are swimming by means of rotating internal or external flagellar filaments or gliding by means of retracting pili. The archaeabacterial flagellar filament differs significantly from the eubacterial flagellum: (1) Its diameter is 10-14 nm, compared to 18-24 nm for eubacterial flagellar filaments. (2) It has 3.3 subunits/turn of a 1.9 nm pitch left-handed helix compared to 5.5 subunits/turn of a 2.6 nm pitch right-handed helix for plain eubacterial flagellar filaments. (3) The archaeabacterial filament is glycosylated, which is uncommon in eubacterial flagella and is believed to be one of the key elements for stabilizing proteins under extreme conditions. (4) The amino acid composition of archaeabacterial flagellin, although highly conserved within the group, seems unrelated to the highly conserved eubacterial flagellins. On the other hand, the archaeabacterial flagellar filament shares some fundamental properties with type IV pili: (1) The hydrophobic N termini are largely homologous with the oligomerization domain of pilin. (2) The flagellin monomers follow a different mode of transport and assembly. They are synthesized as pre-flagellin and have a cleavable signal peptide, like pre-pilin and unlike eubacterial flagellin. (3) The archaeabacterial flagellin, like pilin, is glycosylated. (4) The filament lacks a central channel, consistent with polymerization occurring at the cell-proximal end. (5) The diameter of type IV pili, 6-9 nm, is closer to that of the archaeabacterial filament, 10-14 nm. A large body of data on the biochemistry and molecular biology of archaeabacterial flagella has accumulated in recent years. However, their structure and symmetry is only beginning to unfold. Here, we review the structure of the archaeabacterial flagellar filament in reference to the structures of type IV pili and eubacterial flagellar filaments, with which it shares structural and functional similarities, correspondingly.
常见的原核生物运动模式包括通过旋转内部或外部鞭毛丝进行游动，或者通过收缩菌毛进行滑行。古细菌的鞭毛丝与真细菌的鞭毛有显著差异：（1）其直径为10 - 14纳米，而真细菌鞭毛丝的直径为18 - 24纳米。（2）它是每1.9纳米螺距的左旋螺旋有3.3个亚基/圈，相比之下，普通真细菌鞭毛丝是每2.6纳米螺距的右旋螺旋有5.5个亚基/圈。（3）古细菌的鞭毛丝进行了糖基化，这在真细菌鞭毛中并不常见，并且被认为是在极端条件下稳定蛋白质的关键因素之一。（4）古细菌鞭毛蛋白的氨基酸组成，尽管在该类群中高度保守，但似乎与高度保守的真细菌鞭毛蛋白无关。另一方面，古细菌的鞭毛丝与IV型菌毛具有一些基本特性：（1）疏水的N末端与菌毛蛋白的寡聚化结构域在很大程度上同源。（2）鞭毛蛋白单体遵循不同的运输和组装模式。它们像菌毛蛋白原一样作为前鞭毛蛋白合成，并且有一个可切割的信号肽，这与真细菌鞭毛蛋白不同。（3）古细菌鞭毛蛋白像菌毛蛋白一样进行了糖基化。（4）鞭毛丝缺乏中央通道，这与在细胞近端发生聚合作用一致。（5）IV型菌毛的直径为6 - 9纳米，更接近古细菌鞭毛丝的直径（10 - 14纳米）。近年来积累了大量关于古细菌鞭毛的生物化学和分子生物学数据。然而，它们的结构和对称性才刚刚开始被揭示。在这里，我们参照IV型菌毛和真细菌鞭毛丝的结构来综述古细菌鞭毛丝的结构，与之相应地，古细菌鞭毛丝与它们在结构和功能上具有相似性。
