ジャーナル: J Mol Biol / 年: 2006 タイトル: Three-dimensional structure of a type III glutamine synthetase by single-particle reconstruction. 著者: Jason M van Rooyen / Valerie R Abratt / B Trevor Sewell / 要旨: GlnN, the type III glutamine synthetase (GSIII) from the medically important, anaerobic, opportunistic pathogen Bacteroides fragilis, has 82.8 kDa subunits that share only 9% sequence identity with ...GlnN, the type III glutamine synthetase (GSIII) from the medically important, anaerobic, opportunistic pathogen Bacteroides fragilis, has 82.8 kDa subunits that share only 9% sequence identity with the type I glutamine synthetases (GSI), the only family for which a structure is known. Active GlnN was found predominantly in a single peak that eluted from a calibrated gel-filtration chromatography column at a position equaivalent to 0.86(+/-0.08) MDa. Negative-stain electron microscopy enabled the identification of double-ringed particles and single hexameric rings ("pinwheels") resulting from partial staining. A 2D average of these pinwheels showed marked similarity to the corresponding structures found in preparations of GSI, except that the arms of the subunits were 40% longer. Reconstructions from particles embedded in vitreous ice showed that GlnN has a double-ringed, dodecameric structure with a 6-fold dihedral space group (D6) symmetry and dimensions of 17.0 nm parallel with the 6-fold axis and 18.3 nm parallel with the 2-fold axes. The structures, combined with a sequence alignment based on structural principles, showed how many aspects of the structure of GSI, and most notably the alpha/beta barrel fold active site were preserved. There was evidence for the presence of this structure in the reconstructed volume, thus, identifying the indentations between the pinwheel spokes as putative active sites and suggesting conservation of the overall molecular geometry found in GSI despite their low level of global homology. Furthermore, docking of GSI into the reconstruction left sufficient plausibly located unoccupied density to account for the additional residues in GSIII, thus validating the structure.
タイプ: NEGATIVE 詳細: Aliquots (10ul) were applied to 300 mesh copper grids, which had been coated with thin carbon support film and previously glow discharged in air for 20 seconds, before being stained with 2% ...詳細: Aliquots (10ul) were applied to 300 mesh copper grids, which had been coated with thin carbon support film and previously glow discharged in air for 20 seconds, before being stained with 2% uranyl acetate solution using the droplet method.
グリッド
詳細: 300 mesh copper grid
凍結
凍結剤: ETHANE
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電子顕微鏡法
顕微鏡
FEI TECNAI F20
特殊光学系
エネルギーフィルター - 名称: LEO OMEGA
詳細
Leo 912 TEM
日付
2004年5月13日
撮影
カテゴリ: CCD フィルム・検出器のモデル: PROSCAN TEM-PIV (2k x 2k) デジタル化 - サンプリング間隔: 14 µm / 実像数: 160 詳細: Images were digitized using an Ilford Leafscan and downsized by a factor of 2 ビット/ピクセル: 16