Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208, USA.
Science. 2010 Sep 17;329(5998):1526-30. doi: 10.1126/science.1190187. Epub 2010 Aug 5.
The class Ib ribonucleotide reductase of Escherichia coli can initiate reduction of nucleotides to deoxynucleotides with either a Mn(III)2-tyrosyl radical (Y•) or a Fe(III)2-Y• cofactor in the NrdF subunit. Whereas Fe(III)2-Y• can self-assemble from Fe(II)2-NrdF and O2, activation of Mn(II)2-NrdF requires a reduced flavoprotein, NrdI, proposed to form the oxidant for cofactor assembly by reduction of O2. The crystal structures reported here of E. coli Mn(II)2-NrdF and Fe(II)2-NrdF reveal different coordination environments, suggesting distinct initial binding sites for the oxidants during cofactor activation. In the structures of Mn(II)2-NrdF in complex with reduced and oxidized NrdI, a continuous channel connects the NrdI flavin cofactor to the NrdF Mn(II)2 active site. Crystallographic detection of a putative peroxide in this channel supports the proposed mechanism of Mn(III)2-Y• cofactor assembly.
大肠杆菌的 Ib 核糖核苷酸还原酶可以在 NrdF 亚基中的 Mn(III)2-酪氨酸自由基 (Y•) 或 Fe(III)2-Y•辅助因子的作用下，起始核苷酸还原为脱氧核苷酸。虽然 Fe(III)2-Y•可以通过 Fe(II)2-NrdF 和 O2 自组装，但 Mn(II)2-NrdF 的激活需要一种还原的黄素蛋白 NrdI，据推测，它通过还原 O2 形成辅助因子组装的氧化剂。本文报道的大肠杆菌 Mn(II)2-NrdF 和 Fe(II)2-NrdF 的晶体结构揭示了不同的配位环境，这表明在辅助因子激活过程中，氧化剂可能具有不同的初始结合位点。在与还原和氧化的 NrdI 形成复合物的 Mn(II)2-NrdF 结构中，一个连续的通道将 NrdI 黄素辅因子与 NrdF 的 Mn(II)2 活性位点连接起来。在该通道中检测到的可能过氧化物支持了 Mn(III)2-Y•辅助因子组装的提议机制。
