アンモニアは,光システムIIの酸素進化複合体のより危険なマンガネスと結合する
Paul H Oyala1, Troy A Stich1, Richard J Debus2
1†Department of Chemistry, University of California, Davis, Davis, California 95616, United States.
Journal of the American Chemical Society
|June 18, 2015
まとめ
アンモニアは,写真系IIのマンガン群の端末NH3として結合するが,ブリッジとして結合しない. これは,酸素が進化する複合体における基板結合と二酸化炭素形成のメカニズムを明らかにする.
科学分野:
- バイオケミストリー バイオケミストリー
- 光合成の研究研究である.
- 構造生物学 構造生物学とは
背景:
- 光学系II (PSII) は,酸素による光合成に不可欠である.
- PSIIの水酸化Mn4CaO5クラスターは,水を酸素,陽子,電子に分解する役割を担っています.
- 基板結合部位を特定することは,酸素進化のメカニズムを理解するための鍵です.
研究 の 目的:
- PSIIの酸素進化複合体におけるアンモニア (基板類型) の正確な結合部位を決定する.
- アスパルテート-61の基板結合と水の酸化における役割を調査する.
- ディオキシゲン形成のメカニズムを解明する.
主な方法:
- PSII.の高解像度のX線結晶学.
- パルス電子パラマグネティック共振 (EPR) スペクトロスコピー.
- サイト・ダイレクト・ミュータジェネシス (D1-D61A変異体).
主要な成果:
- X線構造は,Mn4CaO5群の近くの潜在的基板結合部位を特定しました.
- D1タンパク質のアスパルテート-61は,Mn4A部位に結合した主要な水分子 (W1) と水素結合を形成する.
- パルスEPRスペクトルは,アンモニアがNH3としてMn4A部位に結合することを確認し,ブリッジリングリガンドとしてではなく,野生型とD1-D61A変異体PSIIの両方で結合することを確認しました.
結論:
- アンモニアはMn4A部位に末端結合し,橋渡し相互作用に関する以前の仮説に異議を唱える.
- アスパルテート-61とW1の間の水素結合は,この場所での末端アンモニア結合に不可欠ではありません.
- この発見は,基板相互作用とPSIIにおける水の酸化の触媒機構の理解を洗練する.
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