ジャーナル: Nature / 年: 2024 タイトル: Membraneless channels sieve cations in ammonia-oxidizing marine archaea. 著者: Andriko von Kügelgen / C Keith Cassidy / Sofie van Dorst / Lennart L Pagani / Christopher Batters / Zephyr Ford / Jan Löwe / Vikram Alva / Phillip J Stansfeld / Tanmay A M Bharat / 要旨: Nitrosopumilus maritimus is an ammonia-oxidizing archaeon that is crucial to the global nitrogen cycle. A critical step for nitrogen oxidation is the entrapment of ammonium ions from a dilute marine ...Nitrosopumilus maritimus is an ammonia-oxidizing archaeon that is crucial to the global nitrogen cycle. A critical step for nitrogen oxidation is the entrapment of ammonium ions from a dilute marine environment at the cell surface and their subsequent channelling to the cell membrane of N. maritimus. Here we elucidate the structure of the molecular machinery responsible for this process, comprising the surface layer (S-layer), using electron cryotomography and subtomogram averaging from cells. We supplemented our in situ structure of the ammonium-binding S-layer array with a single-particle electron cryomicroscopy structure, revealing detailed features of this immunoglobulin-rich and glycan-decorated S-layer. Biochemical analyses showed strong ammonium binding by the cell surface, which was lost after S-layer disassembly. Sensitive bioinformatic analyses identified similar S-layers in many ammonia-oxidizing archaea, with conserved sequence and structural characteristics. Moreover, molecular simulations and structure determination of ammonium-enriched specimens enabled us to examine the cation-binding properties of the S-layer, revealing how it concentrates ammonium ions on its cell-facing side, effectively acting as a multichannel sieve on the cell membrane. This in situ structural study illuminates the biogeochemically essential process of ammonium binding and channelling, common to many marine microorganisms that are fundamental to the nitrogen cycle.
Movies collected at the scope were clustered into optics groups based on the XML meta-data of the data-collection software EPU (Thermo Fisher Scientific) using a k-means algorithm implemented in EPU_group_AFIS (https://github.com/DustinMorado/EPU_group_AFIS). Imported movies were motion-corrected, dose-weighted, and Fourier cropped (2x) with MotionCor2 implemented in RELION-3.1. Contrast transfer functions (CTFs) of the resulting motion-corrected micrographs were estimated using CTFFIND4.
粒子像選択
選択した数: 1971908 詳細: Initially, side views of S-layer sheets were first manually picked along the edge of the lattice using the helical picking tab in RELION while setting the helical rise to 60 angstrom. Top and ...詳細: Initially, side views of S-layer sheets were first manually picked along the edge of the lattice using the helical picking tab in RELION while setting the helical rise to 60 angstrom. Top and tilted views were manually picked at the central hexameric axis. Manually picked particles were extracted in 4x downsampled 128x128 pixel2 boxes and classified using reference-free 2D classification inside RELION-3.1. Class averages centered at a hexameric axis were used to automatically pick particles inside RELION-3.1. Automatically picked particles were extracted in 4x downsampled 128x128 pixel2 boxes and classified using reference-free 2D classification. Particle coordinates belonging to class averages centered at the hexameric axis were used to train TOPAZ in 5x downsampled micrographs with the neural network architecture conv127. For the final reconstruction, particles were picked using TOPAZ and the previously trained neural network above. Additionally, top, bottom, and side views were picked using the reference-based autopicker inside RELION-3.1, which TOPAZ did not readily identify. Particles were extracted in 4x downsampled 128x128 pixel2 boxes and classified using reference-free 2D classification inside RELION-3.1. Particles belonging to class averages centered at the hexameric axis were combined, and particles within 30 angstrom were removed to prevent duplication after alignment. All resulting particles were then re-extracted in 4x downsampled 128x128 pixel2 boxes.
初期モデル
モデルのタイプ: NONE 詳細: All side views and a subset of top and bottom views were used for initial model generation in RELION-3.1. The scaled and lowpass filtered output was then used as a starting model for 3D auto ...詳細: All side views and a subset of top and bottom views were used for initial model generation in RELION-3.1. The scaled and lowpass filtered output was then used as a starting model for 3D auto refinement in a 512x512 pixel box.
最終 再構成
想定した対称性 - 点群: C2 (2回回転対称) / アルゴリズム: FOURIER SPACE / 解像度のタイプ: BY AUTHOR / 解像度: 2.71 Å / 解像度の算出法: FSC 0.143 CUT-OFF / ソフトウェア - 名称: RELION (ver. 3.1) 詳細: Per-particle defocus, anisotropy magnification, and higher-order aberrations were refined inside RELION3.1, followed by three rounds of focused 3D auto refinement. Bayesian particle polishing ...詳細: Per-particle defocus, anisotropy magnification, and higher-order aberrations were refined inside RELION3.1, followed by three rounds of focused 3D auto refinement. Bayesian particle polishing was performed subsequently in a 640x640 pixel2 box followed by auto-refinement and symmetry relaxation. The final map was obtained from 354,860 particles and post-processed using a soft mask focused on the central hexamer, yielding a global resolution of 2.7 angstrom according to the Fourier shell correlation criterion between two independently refined half-maps at a threshold value at 0.143, and local resolution up to 2.5 angstrom 使用した粒子像数: 354860
初期 角度割当
タイプ: MAXIMUM LIKELIHOOD / ソフトウェア - 名称: RELION (ver. 3.1) / 詳細: Angle assignment was performed within RELION3.1
最終 角度割当
タイプ: MAXIMUM LIKELIHOOD / ソフトウェア - 名称: RELION (ver. 3.1) / 詳細: Angle assignment was performed within RELION3.1
最終 3次元分類
ソフトウェア - 名称: RELION (ver. 3.1)
FSC曲線 (解像度の算出)
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原子モデル構築 1
精密化
空間: RECIPROCAL / プロトコル: AB INITIO MODEL / 温度因子: 41.4 / 当てはまり具合の基準: Best Fit
得られたモデル
PDB-8c8l: In vitro structure of the Nitrosopumilus maritimus S-layer - Two-fold symmetry (C2)