コクの光合成水酸化クロックの中間物質の構造

Jan Kern¹, Ruchira Chatterjee¹, Iris D Young¹

¹Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.

Nature

|November 9, 2018

まとめ

研究者はX線結晶学を用いて光合成酸素の進化サイクルのすべての状態を視覚化しました O−O結合形成の特定のメカニズムを除いて,酸素生産に関与する重要な水分子を特定しました.

科学分野:

生物化学
光合成の研究
構造生物学

背景:

生命にとって不可欠な光合成酸素の進化はコークのS状態サイクルに従っています
光システムII (PSII) の酸素進化複合体 (OEC) には,水の酸化を担う Mn4CaO5 クラスタが含まれています.
O-O結合形成の正確なメカニズムを理解することは,光合成の研究における重要な課題です.

研究の目的:

高解像度でPSIIのKokのS状態サイクルのすべての (メタ) 安定状態を視覚化します.
触媒サイクル中の一時的な構造変化を捉えるために
水酸化におけるO−O結合形成と基板配送のメカニズムを解明する.

主な方法:

室温での連続フェムト秒X線結晶学 (SFX)
マルチフラッシュ可視レーザー刺激による同時X線放射スペクトロスコーピー (XES).
OECの (メタ) 安定状態と一時的な状態の高解像度構造的決定

主要な成果:

すべての (メタ) 安定したS0-S3状態の高解像度構造 (2.042.08 Å) が得られた.
150 と 400 μs の2つの一時的な状態の構造は,重要な構造的動態を明らかにした.
Ca と Mn1 の間に位置する S2→S3 移行中に追加の酸素原子 (Ox) の結合が観察されました.
水リンガンドW3は,潜在的に基板配送に関与していることが確認された.

結論:

S3状態のOxの結合は,O5が基板であり,Oxが第2基板であるか,またはO2の放出後にO5の位置を補充するメカニズムをサポートします.
S3状態でのペロキシ結合形成は排除されている.
W3とW2を含む核愛性の攻撃メカニズムは,O−O結合の形成にはありそうにない.

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