非ヘムFe (II) ハロゲナーゼSyrB2の反応性に関する第一原理研究
Heather J Kulik1, Leah C Blasiak, Nicola Marzari
1Department of Materials Science & Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA. hjkulik@mit.edu
Journal of the American Chemical Society
|October 8, 2009
まとめ
計算による研究では,SyrB2ハロゲナーゼ酵素の機能が明らかになりました. この研究では,アルファ-ケトグルタレートのデカルボキシル化が容易であるが,水素抽出にはバリアがあるが,塩素化にはバリアがなく,水素抽出と結合していることが示されている.
科学分野:
- バイオケミストリーと酵素学
- 計算化学はコンピュータ化学である.
- バイオ・オーガニック化学
背景:
- SyrB2は,シリンゴマイシン生物合成に関与するアルファケトグルタレート (alphaKG) 依存型ハロゲナーゼです.
- ハロゲナーゼとヒドロキシラーゼは,構造的および化学的類似性を共有しているが,アルファKGデカルボキシル化後の触媒機構では異なっている.
- 変異研究では,ハロゲナーゼとヒドロキシラーゼの活動が相互に変換されず,異なるメカニズム的要件が示唆されています.
研究 の 目的:
- SyrB2酵素活性部位の反応機構を計算的に調査する.
- モデル複合体を用いて,可能性のある反応経路を探索し,ハロゲナーゼ活性を制御する重要なステップを特定する.
- 触媒サイクルにおける個々のステップのエネルギー貢献とそれらの結合を解明する.
主な方法:
- Fe (II) 化学の正確なモデリングのためのハバードU補正による密度関数理論 (DFT) 計算.
- 鉄の中心部とその直接リガンドからなる簡素化されたモデル複合体を利用した.
- アルファKGデカルボキシル化,水素抽出,およびラジカル塩素化/水酸化を含む反応経路を分析した.
主要な成果:
- アルファ-ケトグルタレートのデカルボキシル化は,バリアのない,エクソサーミックな初期段階です.
- 水素抽出は,生物学的アクセス可能なエネルギーバリアを示し,塩素化と組み合わせると減少します.
- ラジカルクロリネーションはバリアレスでエクソテルミックであり,類似した水酸化はモデルシステムで小さなエネルギーバリアを持っています.
結論:
- クロリネーションのエネルギー的な好みと,水素抽出との結合が,ハロゲナーゼの活性性を説明する.
- 変異したヒドロキシラゼは,基板への結合が悪いため,塩素化が欠けている可能性が高いが,変異したハロゲネゼは,エネルギー障壁のためにヒドロキシラートできない.
- 活性部位の最小限のモデル複合体は,ハロゲナース反応性の重要な側面を効果的に説明することができます.
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