Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom.
Proc Natl Acad Sci U S A. 2023 Apr 18;120(16):e2215808120. doi: 10.1073/pnas.2215808120. Epub 2023 Apr 12.
is an atypical diderm bacterium with a remarkable ability to tolerate various environmental stresses, due in part to its complex cell envelope encapsulated within a hyperstable surface layer (S-layer). Despite decades of research on this cell envelope, atomic structural details of the S-layer have remained obscure. In this study, we report the electron cryomicroscopy structure of the S-layer, showing how it is formed by the Hexagonally Packed Intermediate-layer (HPI) protein arranged in a planar hexagonal lattice. The HPI protein forms an array of immunoglobulin-like folds within the S-layer, with each monomer extending into the adjacent hexamer, resulting in a highly interconnected, stable, sheet-like arrangement. Using electron cryotomography and subtomogram averaging from focused ion beam-milled cells, we have obtained a structure of the cellular S-layer, showing how this HPI S-layer coats native membranes on the surface of cells. Our S-layer structure from the diderm bacterium shows similarities to immunoglobulin-like domain-containing S-layers from monoderm bacteria and archaea, highlighting common features in cell surface organization across different domains of life, with connotations on the evolution of immunoglobulin-based molecular recognition systems in eukaryotes.
是一种非典型的双菌，具有卓越的耐受各种环境压力的能力，部分原因在于其复杂的细胞包膜被包裹在超稳定的表面层（S-层）内。尽管对该细胞包膜进行了数十年的研究，但 S-层的原子结构细节仍然不清楚。在这项研究中，我们报告了 S-层的电子 cryomicroscopy 结构，展示了它如何由排列在平面六方晶格中的六边形中间层（HPI）蛋白形成。HPI 蛋白在 S-层内形成一系列免疫球蛋白样折叠，每个单体延伸到相邻的六聚体中，从而形成高度互连、稳定、片状排列。使用电子 cryotomography 和来自聚焦离子束铣削细胞的子断层平均化，我们获得了细胞 S-层的结构，展示了 HPI S-层如何在细胞表面涂覆天然膜。我们从双菌中获得的 S-层结构与单菌和古菌中含有免疫球蛋白样结构域的 S-层相似，突出了不同生命领域中细胞表面组织的共同特征，对真核生物中基于免疫球蛋白的分子识别系统的进化具有启示意义。
