School of Chemistry and Biochemistry, University of Western Australia, Crawley, Western Australia, 6009 Australia.
Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, United States of America.
Sci Rep. 2017 Jan 18;7:40517. doi: 10.1038/srep40517.
The protein microenvironment surrounding the flavin cofactor in flavoenzymes is key to the efficiency and diversity of reactions catalysed by this class of enzymes. X-ray diffraction structures of oxidoreductase flavoenzymes have revealed recurrent features which facilitate catalysis, such as a hydrogen bond between a main chain nitrogen atom and the flavin redox center (N5). A neutron diffraction study of cholesterol oxidase has revealed an unusual elongated main chain nitrogen to hydrogen bond distance positioning the hydrogen atom towards the flavin N5 reactive center. Investigation of the structural features which could cause such an unusual occurrence revealed a positively charged lysine side chain, conserved in other flavin mediated oxidoreductases, in a second shell away from the FAD cofactor acting to polarize the peptide bond through interaction with the carbonyl oxygen atom. Double-hybrid density functional theory calculations confirm that this electrostatic arrangement affects the N-H bond length in the region of the flavin reactive center. We propose a novel second-order partial-charge interaction network which enables the correct orientation of the hydride receiving orbital of N5. The implications of these observations for flavin mediated redox chemistry are discussed.
黄素辅酶周围的蛋白质微环境是这类酶催化效率和多样性的关键。氧化还原酶黄素酶的 X 射线衍射结构揭示了促进催化的反复出现的特征，例如主链氮原子和黄素氧化还原中心（N5）之间的氢键。胆固醇氧化酶的中子衍射研究揭示了一个不寻常的拉长主链氮氢键距离，将氢原子定位在黄素 N5 反应中心附近。对可能导致这种不寻常情况的结构特征的研究表明，在远离 FAD 辅因子的第二壳层中存在一个带正电荷的赖氨酸侧链，在其他黄素介导的氧化还原酶中保守，通过与羰基氧原子相互作用来极化肽键。双杂交密度泛函理论计算证实，这种静电排列会影响黄素反应中心区域的 N-H 键长。我们提出了一种新的二阶部分电荷相互作用网络，使 N5 的氢化物接受轨道能够正确定向。这些观察结果对黄素介导的氧化还原化学的影响进行了讨论。
