アセチル共酵素aシンタゼに対するZnの作用:カタリシス中のアルファサブユニットにおける構成変化の証拠
Xiangshi Tan1, Matthew R Bramlett, Paul A Lindahl
1Department of Chemistry, Texas A & M University, College Station, Texas 77843, USA.
Journal of the American Chemical Society
|May 13, 2004
まとめ
亜鉛 (Zn) は,不活性なニップ金属部位を置換することによって,アセチル-コア合成酶 (ACS) を無効化する. このZn誘発の無活性化は,触媒作用中に発生し,ACSアルファサブユニットの構成の変化が,そのメカニズムにとって決定的であることを示唆しています.
科学分野:
- バイオケミストリー バイオケミストリー
- 酵素学 酵素学とは
- バイオ・オーガニック化学 バイオ・オーガニック化学
背景:
- アセチル-コア合成酵素 (ACS) は,複合的な活性部位 (A-クラスタ) を有するアルファ2β2テトラメアです.
- A-クラスターには,アルファ亜単位内の {Nip Nid} 双核部位に架け付けられた Fe4S4 キューバンが含まれています.
- アルファ亜単位は,開いた (Nip 露出) と閉じた (Nip 埋葬) 構成で存在し,Nip は銅 (Cu) などの他の金属で置き換えることができます.
研究 の 目的:
- 亜鉛 (Zn) がアセチル-コア合成酵素 (ACS) の構造と機能に及ぼす影響を調査する.
- ZnがACS活性部位と相互作用するメカニズムと条件を決定する.
主な方法:
- 酵素活性アッセイは,コリノイド鉄硫黄タンパク質 (CoFeSP) からメチル群の受容性を測定する.
- 電子パラマグネティック共振 (EPR) スペクトロスコピーは,NiFeC信号を検出する.
- ニップのZn置換の運動分析.
主要な成果:
- ニップのZn置換はACSを無効にし,メチル群の受容とNiFeC EPR信号を妨げます.
- Zn-bound ACSは,Niを加えることで再活性化することはできません.
- Znは,特に触媒の過程でNipを代用し,中間の触媒状態が感受性があることを示唆しています.
- Znの置換はEDTAによって阻害され,金属に依存するプロセスを示しています.
結論:
- Znは,Znの低い核好性による可能性が高い,不安定なNip部位を不可逆的に置き換えることで,ACSを無効化する.
- Zn-Nipの相互作用は形状に依存し,アルファ亜単位が開かれた状態にあるときに発生します.
- ACSアルファサブユニットにおける触媒に依存する構成変化は,機械的な役割を果たし,オープン構成はZn攻撃に敏感である.
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