Archaea share genomic similarities with Eukarya and cellular architectural similarities with Bacteria, though archaeal and bacterial surface layers (S-layers) differ. Using cellular cryo–electron tomography, we visualized the S-layer lattice surrounding Methanospirillum hungatei , a methanogenic archaeon. Though more compact than known structures, M. hungatei ’s S-layer is a flexible hexagonal lattice of dome-shaped tiles, uniformly spaced from both the overlying cell sheath and the underlying cell membrane. Subtomogram averaging resolved the S-layer hexamer tile at 6.4-angstrom resolution. By fitting an AlphaFold model into hexamer tiles in flat and curved conformations, we uncover intra- and intertile interactions that contribute to the S-layer’s cylindrical and flexible architecture, along with a spacer extension for cell membrane attachment. M. hungatei cell’s end plug structure, likely composed of S-layer isoforms, further highlights the uniqueness of this archaeal cell. These structural features offer advantages for methane release and reflect divergent evolutionary adaptations to environmental pressures during early microbial emergence.

中文翻译：

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Methanospirillum hungatei 细胞包膜和表层的组成和原位结构


古细菌与真核生物具有基因组相似性，与细菌的细胞结构相似性，尽管古细菌和细菌表面层 （S 层） 不同。使用细胞冷冻电子断层扫描，我们可视化了 Methanospirillum hungatei 周围的 S 层晶格，这是一种产甲烷古细菌。虽然比已知的结构更紧凑，但 M. hungatei 的 S 层是一个由圆顶形瓷砖组成的柔性六边形晶格，与上覆的细胞鞘和下面的细胞膜均匀间隔。亚断层图平均以 6.4 埃的分辨率解析 S 层六聚体平铺。通过将 AlphaFold 模型拟合到平面和弯曲构象的六聚体瓦片中，我们揭示了有助于 S 层圆柱形和柔性结构的瓦片内和瓦间相互作用，以及用于细胞膜附着的间隔延伸。M. hungatei 细胞的末端栓结构可能由 S 层亚型组成，进一步突出了这种古细菌细胞的独特性。这些结构特征为甲烷释放提供了优势，并反映了微生物早期出现期间对环境压力的不同进化适应。