GDP-マノース-3',5'-エピメラーゼの構造と機能:同じ活性部位で3つの化学反応を行う酵素

Louise L Major¹, Beata A Wolucka, James H Naismith

¹Centre for Biomolecular Sciences, University of St. Andrews, North Haugh, St. Andrews, Fife, Scotland KY16 9ST, United Kingdom.

Journal of the American Chemical Society

|December 22, 2005

まとめ

アラビドプシス・タリアナ GDP-マノゼ-3

科学分野:

バイオケミストリーバイオケミストリー
構造生物学構造生物学とは
植物科学植物科学について

背景:

GDP-マノース-3',5'-エピメラーゼ (GME) は,植物におけるビタミンCの生物合成に不可欠である.
GMEはGDP-α-D-マノースをGDP-β-L-ガラクトースに変換する触媒となる.
この酵素はまた,C5'エピマーであるGDP-β-L-グルースも生成する.

研究の目的:

GMEの触媒機構の構造的基礎を解明する.
GDP-α-D-マノースの二重エピメリゼーションを理解するために.
ビタミンCの合成における酵素の役割を調査する.

主な方法:

GME複合体のX線結晶学,基板と産物.
サイト・ディレクテッド・ミュータゲネシスで,主要な触媒残基を特定する.
酵素活性と産物形成を確認するための生化学分析.

主要な成果:

GME複合体の高解像度構造を決定し,古典的な短鎖脱水素酶/還元酶 (SDR) 折り目を明らかにした.
確認されたGMEは,GDP-β-L-ガラクトーゼとGDP-β-L-ガラクトーゼの間の均衡を確立します.
エピメリゼーションに責任を負う触媒酸/塩基ペア (C145とK217) を特定しました.
C4'酸化,C5'エピメリゼーション,およびその後の還元またはC3'エピメリゼーションを含む反応機構を提案した.

結論:

GMEは,酸化,エピメリゼーション,還元のために単一の活性部位を使用しており,これは珍しい触媒戦略です.
構造的洞察は,触媒処理中に特定の中間物質と構成の変化を示唆しています.
この発見は,植物ビタミンCのバイオシンセシスの重要なステップの詳細な分子理解を提供します.

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