リドックス依存メタスタビリティの P-クラスター
Hannah L Rutledge1, Jonathan Rittle1, Laura M Williamson1
1Department of Chemistry and Biochemistry , University of California, San Diego , 9500 Gilman Drive , La Jolla , California 92093-0356 , United States.
Journal of the American Chemical Society
|June 1, 2019
まとめ
モリブデンナイトロゲンゼのPクラスターは,酸素リガンドなしで酸化すると鉄原子を失うが,それでも窒素を減少させる. この可変性は,窒素酶機能における電子移転の鍵となる.
科学分野:
- 生物化学
- バイオ有機化学
- 酵素メカニズム
背景:
- モリブデン窒素酵素は,生命にとって不可欠なプロセスである,二酸化窒素 (N2) をアンモニア (NH3) に変換することを促進する.
- 活性部位コファクター (FeMoco) への電子転送には,モリブデン鉄タンパク質 (MoFeP) 内にある [8Fe-7S] クラスター (P-クラスター) が含まれる.
- P-クラスターは,酸化時に構造変化を起こし,酸素リガンド (SerまたはTyr) を含み,電子の移転に影響を及ぼします.
研究 の 目的:
- Azotobacter vinelandii (Av) MoFePのPクラスターにおける酸素リガンドの役割を調査する.
- 酸素リガンドの除去または変化がP-クラスターの安定性および窒素酵素の活性にどのように影響するかを決定する.
- Av MoFePのPクラスター環境とGluconacetobacter diazotrophicus (Gd) MoFePのPクラスター環境を比較する.
主な方法:
- Av MoFePの変種を生成するサイト指向型変異:βSer188Ala (酸素リガンドなし),βPhe99Tyr/βSer188Ala (Gdのような環境),およびβPhe99Tyr (酸素リガンド2種).
- 窒素酵素の活性を評価する生化学的測定
- P-クラスタの安定性と組成を特徴づけるために,スペクトル解析と構造分析を行う.
主要な成果:
- P-クラスターは,酸素リガンドの不在で酸化時に構成的に不安定になり,Feセンターを逆転的に失います.
- 酸素リガンドが欠けていた変種は,野生型のような二酸化窒素還元活性を維持した.
- AvとGd MoFePは,それぞれSerとTyrリガンドに対する明確な好みを示し,特定の進化的適応を示しています.
結論:
- P-クラスタの組成の不安定さは,特に酸素リガンドがない場合,マルチ電子反応を可能にする酸化還元結合型変化に不可欠である.
- MoFePの酸素リガンドの構造的制御は,直接の調整球を超えています.
- 不安定なFe-Sクラスターは,金属酵素における複雑な酸化還元プロセスを促進する一般的な特徴である.
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