ジャーナル: Nature / 年: 2000 タイトル: Molecular mechanism of vectorial proton translocation by bacteriorhodopsin. 著者: S Subramaniam / R Henderson / 要旨: Bacteriorhodopsin, a membrane protein with a relative molecular mass of 27,000, is a light driven pump which transports protons across the cell membrane of the halophilic organism Halobacterium ...Bacteriorhodopsin, a membrane protein with a relative molecular mass of 27,000, is a light driven pump which transports protons across the cell membrane of the halophilic organism Halobacterium salinarum. The chromophore retinal is covalently attached to the protein via a protonated Schiff base. Upon illumination, retinal is isomerized. The Schiff base then releases a proton to the extracellular medium, and is subsequently reprotonated from the cytoplasm. An atomic model for bacteriorhodopsin was first determined by Henderson et al, and has been confirmed and extended by work in a number of laboratories in the last few years. Here we present an atomic model for structural changes involved in the vectorial, light-driven transport of protons by bacteriorhodopsin. A 'switch' mechanism ensures the vectorial nature of pumping. First, retinal unbends, triggered by loss of the Schiff base proton, and second, a protein conformational change occurs. This conformational change, which we have determined by electron crystallography at atomic (3.2 A in-plane and 3.6 A vertical) resolution, is largely localized to helices F and G, and provides an 'opening' of the protein to protons on the cytoplasmic side of the membrane.
履歴
登録
2000年7月15日
登録サイト: RCSB / 処理サイト: RCSB
改定 1.0
2000年8月9日
Provider: repository / タイプ: Initial release
改定 1.1
2008年4月27日
Group: Version format compliance
改定 1.2
2011年7月13日
Group: Derived calculations / Version format compliance
∠γ: 120 ° / A: 62.45 Å / B: 62.45 Å / C: 100.9 Å / Space group name H-M: P3
-
試料調製
構成要素
名称: CYTOPLASMICALLY OPEN CONFORMATION OF BACTERIORHODOPSIN 由来: RECOMBINANT
分子量
値: .027 MDa / 実験値: NO
由来(天然)
生物種: Halobacterium salinarum (好塩性)
試料
包埋: YES / シャドウイング: NO / 染色: NO / 凍結: YES
EM embedding
Material: glucose or trehalose
結晶化
温度: 310 K / 手法: naturally occurring in vivo / pH: 7 詳細: crystals are increased in size by fusion and annealing using detergents, pH 7, naturally occurring in vivo, temperature 37K
結晶化
*PLUS
温度: 4 ℃ / pH: 5.6 / 手法: unknown
溶液の組成
*PLUS
ID
濃度
一般名
Crystal-ID
Sol-ID
1
18-23 mg/ml
protein
1
1
2
0.5 %(w/v)
beta-octylglucopyranoside
1
1
3
4 %(w/v)
benzamidine
1
1
4
1.75M
sodiumphosphate
1
1
5
1.8-2.3 M
ammoniumsulfate
1
reservoir
-
データ収集
顕微鏡
モデル: FEI/PHILIPS CM12 / 詳細: imaging date 1998-12-01
電子銃
照射モード: FLOOD BEAM
電子レンズ
モード: DIFFRACTION
撮影
フィルム・検出器のモデル: GENERIC CCD / Num. of diffraction images: 1000
回折
平均測定温度: 93 K
放射光源
由来: ELECTRON MICROSCOPE / タイプ: OTHER / 波長: 0.033
検出器
タイプ: OTHER / 検出器: CCD / 日付: 1998年12月1日
放射
プロトコル: SINGLE WAVELENGTH / 単色(M)・ラウエ(L): M / 散乱光タイプ: electron
∠γ: 120 ° / A: 62.45 Å / B: 62.45 Å / C: 100.9 Å / Space group name H-M: P3
3次元再構成
解像度: 3.2 Å / 解像度の算出法: DIFFRACTION PATTERN/LAYERLINES 詳細: 402 patterns merged (merging R 17.3%) to generate set of lattice lines covering ~87% of reciprocal space, with resolution of 3.2 A in-plane and 3.6 A vertically [primary citation]
精密化
解像度: 3.2→200 Å / 立体化学のターゲット値: Engh & Huber 詳細: Each diffraction pattern was automatically indexed, and the spot intensities were integrated either using a raster (for patterns recorded at specimen tilts less than 30 degrees) or using ...詳細: Each diffraction pattern was automatically indexed, and the spot intensities were integrated either using a raster (for patterns recorded at specimen tilts less than 30 degrees) or using profile fitting (for patterns recorded at specimen tilts at or greater than 30 degrees, which represented about 80% of the total data set). Each pattern was then compared to the curves recorded for wild-type bacteriorhodopsin in glucose at -100 degrees C [Ceska and Henderson J. Mol. Biol. 213: 539-560 (1990)], and the relative proportions of the four different twins determined. This exercise was carried out with all four theoretically possible orientations of the crystal axes relative to the previous reference curves to ensure that the data were merged correctly. From the initial set of 486 patterns chosen, 286 minimally twinned diffraction patterns were selected in which the major twin proportion was greater than 0.8. These 286 patterns were merged using the wild-type lattice lines as a reference and lattice lines were fitted to the data to obtain an initial approximately merged set of lattice lines (merge #1) describing the structure of the triple mutant. The original set of 486 patterns was then merged against the new lattice curves to redetermine the twin proportions more accurately. The merging parameters for each crystal were inspected carefully again, and 84 crystals for which the major twin proportion was less than 0.70 were excluded from the data set. The remaining 402 substantially untwinned diffraction patterns were used to generate a new set of curves and the procedure repeated to create a stable set of lattice lines. The merged data were further improved by using an estimate of sigma values for each reflection, and by the inclusion of an individual weighting factor for each diffraction pattern using procedures described by Grigorieff and Henderson [Ultramicroscopy 60: 295-309 (1995)]. Two cycles of this refinement were carried out to obtain a final set of merged curves. The curves were sampled at 1/100 Angstroms (approximately twice the thickness of the membrane) to obtain a set of intensities at H,K,L values so that the data could be further processed with standard X-ray crystallographic programs. For the tilt angles used, the maximal possible theoretical completeness of the data set is ~87%. The completeness of our data is close to this limit up to 3.5 Angstroms. The completeness drops to 77.7 % when all of the data to 3.2 Angstroms is included.