Department of Bioengineering, University of California, Los Angeles (UCLA), Los Angeles, CA, 90095, USA.
California NanoSystems Institute, UCLA, Los Angeles, CA, 90095, USA.
Nat Commun. 2023 Oct 23;14(1):6720. doi: 10.1038/s41467-023-42368-2.
Certain archaeal cells possess external proteinaceous sheath, whose structure and organization are both unknown. By cellular cryogenic electron tomography (cryoET), here we have determined sheath organization of the prototypical archaeon, Methanospirillum hungatei. Fitting of Alphafold-predicted model of the sheath protein (SH) monomer into the 7.9 Å-resolution structure reveals that the sheath cylinder consists of axially stacked β-hoops, each of which is comprised of two to six 400 nm-diameter rings of β-strand arches (β-rings). With both similarities to and differences from amyloid cross-β fibril architecture, each β-ring contains two giant β-sheets contributed by ~ 450 SH monomers that entirely encircle the outer circumference of the cell. Tomograms of immature cells suggest models of sheath biogenesis: oligomerization of SH monomers into β-ring precursors after their membrane-proximal cytoplasmic synthesis, followed by translocation through the unplugged end of a dividing cell, and insertion of nascent β-hoops into the immature sheath cylinder at the junction of two daughter cells.
某些古菌细胞具有外部的蛋白质鞘，其结构和组织尚不清楚。通过细胞冷冻电子断层扫描（cryoET），我们确定了原型古菌 Methanospirillum hungatei 的鞘结构。将 Alphafold 预测的鞘蛋白（SH）单体模型拟合到 7.9 Å 分辨率的结构中，表明鞘圆柱体由轴向堆叠的β环组成，每个β环由两到六个 400nm 直径的β链拱（β-环）组成。鞘的每个β-环都含有两个由~450 个 SH 单体组成的巨大β-片层，它们完全环绕细胞的外周。未成熟细胞的断层扫描图像表明了鞘生物发生的模型：在细胞质近端合成后，SH 单体寡聚化为β-环前体，然后通过正在分裂的细胞未堵塞的末端易位，并将新生的β-环插入两个子细胞连接处的未成熟鞘圆柱体中。
