ザンチン酸化還元酵素酸の酵素活性に対するタンパク質構成ゲート
Hiroshi Ishikita1, Bryan T Eger, Ken Okamoto
1Career-Path Promotion Unit for Young Life Scientists, Kyoto University, 202 Building E, Graduate School of Medicine, Kyoto 606-8501, Japan. hiro@cp.kyoto-u.ac.jp
Journal of the American Chemical Society
|December 8, 2011
まとめ
ザンチン酸化還元酵素 (XDH / XO) 酵素は,同一の構造にもかかわらず,電子の転送が異なります. フラビン部位近くのループ構成の変化は,XDHとXOの酸化還元電位の違いを説明する.
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
- 構造生物学 構造生物学とは
背景:
- 哺乳類のキサンチン酸化還元酵素は,キサンチン脱水酸化酵素 (XDH) とキサンチン酸化酵素 (XO) として存在します.
- 両酵素とも共通のリドックス共因子を共有し,電子移転 (ET) 経路を形成し,フラビン共因子で終わります.
- XDHとXOは,同一の原始構造にもかかわらず,フラビンセミキノン/ヒドロキノンペア (E(sq/hq)) の有意な~170mVの酸化還元ポテンシャル差を示しています.
研究 の 目的:
- XDHとXOの異なる電子伝送活動の構造的およびエネルギー的基礎を明らかにする.
- 酵素がFeS-IIからXDHのフラビンへ,NADなしで,エネルギー的に上り坂の電子移転をどのように促進するのかを理解する.
主な方法:
- XDH,XO,NADHの新しい結晶構造に基づくE ((sq/hq) 値の計算と,最大1.65 Åの解像度でのNAD ((+) -/NADH複合のXDHの計算.
- 構造変化の分析と,その影響がフラビン共因子による酸化還元能力に及ぼす影響.
主要な成果:
- XDHとXOのE{\sq/hq}差の主要な原因は,フラビン結合部位 (残留物423-433) 近くのループの構造変化であり,セミキノン状態の安定性に影響する.
- NAD (((+) がXDHと結合することは,大きな構造の変化を誘導しませんでした.
- NADの結合にE{\sq/hq}を変化させる主な要因は,NADの陽性電荷,Asp429のデプロトネーション,およびflavin表面のNADのキャピングである.
結論:
- フラビン部位近くの微妙なループ形状の変化は,XDHとXOの関数的還元電位差の主要な原動力である.
- NAD (((+) 結合は,主要な構造的再編成ではなく,静電性およびステリック相互作用を通じて,XDHにおけるフラビン還酸化ポテンシャルを調節する.
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