Dey Abhishek, Jenney Francis E, Adams Michael W W, Babini Elena, Takahashi Yasuhiro, Fukuyama Keiichi, Hodgson Keith O, Hedman Britt, Solomon Edward I
Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
Science. 2007 Nov 30;318(5855):1464-8. doi: 10.1126/science.1147753.
A persistent puzzle in the field of biological electron transfer is the conserved iron-sulfur cluster motif in both high potential iron-sulfur protein (HiPIP) and ferredoxin (Fd) active sites. Despite this structural similarity, HiPIPs react oxidatively at physiological potentials, whereas Fds are reduced. Sulfur K-edge x-ray absorption spectroscopy uncovers the substantial influence of hydration on this variation in reactivity. Fe-S covalency is much lower in natively hydrated Fd active sites than in HiPIPs but increases upon water removal; similarly, HiPIP covalency decreases when unfolding exposes an otherwise hydrophobically shielded active site to water. Studies on model compounds and accompanying density functional theory calculations support a correlation of Fe-S covalency with ease of oxidation and therefore suggest that hydration accounts for most of the difference between Fd and HiPIP reduction potentials.
生物电子转移领域中一个长期存在的谜题是，高电位铁硫蛋白（HiPIP）和铁氧化还原蛋白（Fd）活性位点中保守的铁硫簇基序。尽管存在这种结构相似性，但HiPIP在生理电位下发生氧化反应，而Fd则被还原。硫K边X射线吸收光谱揭示了水合作用对这种反应性变化的重大影响。天然水合的Fd活性位点中的Fe-S共价性比HiPIP中的低得多，但在脱水后会增加；同样，当展开使原本疏水屏蔽的活性位点暴露于水时，HiPIP共价性会降低。对模型化合物的研究以及伴随的密度泛函理论计算支持Fe-S共价性与氧化难易程度的相关性，因此表明水合作用是Fd和HiPIP还原电位差异的主要原因。
