Browsing by Author "Yu, LJ"

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    An extended N-H bond, driven by a conserved second-order interaction, orients the flavin N5 orbital in cholesterol oxidase
    (Springer Nature, 2017-01-18) Golden, EA; Yu, LJ; Meilleur, F; Blakeley, MP; Duff, AP; Karton, A; Vrielink, A
    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.© The Authors - Creative Commons Attribution 4.0 International License
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    Fluctuation history of the interior East Antarctic ice sheet since mid-pliocene
    (Cambridge University Press, 2008-04) Huang, FX; Liu, XH; Kong, P; Fink, D; Ju, YT; Fang, AM; Yu, LJ; Li, XL; Na, CG
    Cosmogenic Be-10 and Al-26 measurements from bedrock exposures in East Antarctica provide indications of how long the rock surface has been free from glacial cover. Samples from the crests of Zakharoff Ridge and Mount Harding, two typical nunataks in the Grove Mountains, show minimum Be-10 ages of 2.00 +/- 0.22 and 2.30 +/- 0.26 Ma, respectively. These ages suggest that the crests were above the ice sheet at least since the Plio -Pleistocene boundary. Adopting a 'reasonable' erosion rate of 5-10 cm Ma(-1) increases the exposure ages of these two samples to extend into the mid-Pliocene. The bedrock exposure ages steadily decrease with decreasing elevation on the two nunataks, which indicates similar to 200 m decrease of the ice sheet in the Grove Mountains since mid-Pliocene time. Seven higher elevation samples exhibit a simple exposure history, which indicates that the ice sheet in the Grove Mountains decreased only similar to 100 in over a period as long as 1-2 Ma. This suggests that the East Antarctic Ice Sheet (EAIS) was relatively stable during the Pliocene warm interval. Five lower elevation samples suggest a complex exposure history, and indicate that the maximum subsequent increase of the EAIS was only 100 in higher than the present ice surface. Considering the uncertainties, their total initial exposure and subsequent burial time could be later than mid-Pliocene, which may not conflict with the stable mid-Pliocene scenario. © 2008, Cambridge University Press
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    Minimum bedrock exposure ages and their implications: Larsemann Hills and neighboring Bolingen Islands, East Antarctica
    (Wiley-Blackwell, 2010-06-01) Huang, FX; Li, GW; Liu, XH; Kong, P; Ju, YT; Fink, D; Fang, AM; Yu, LJ
    Considerable controversy exists over whether or not extensive glaciation occurred during the global Last Glacial Maximum (LGM) in the Larsemann Hills. In this study we use the in situ produced cosmogenic nuclide 10Be (half life 1.51 Ma) to provide minimum exposure ages for six bedrock samples and one erratic boulder in order to determine the last period of deglaciation in the Larsemann Hills and on the neighboring Bolingen Islands. Three bedrock samples taken from Friendship Mountain (the highest peak on the Mirror Peninsula, Larsemann Hills; ∼2 km from the ice sheet) have minimum exposure ages ranging from 40.0 to 44.7 ka. The erratic boulder from Peak 106 (just at the edge of the ice sheet) has a younger minimum exposure age of only 8.8 ka. The minimum exposure ages for two bedrock samples from Blundell Peak (the highest peak on Stornes Peninsula, Larsemann Hills; ∼2 km from the ice sheet) are about 17 and 18 ka. On the Bolingen Islands (southwest to the Larsemann Hills; ∼10 km from the ice sheet), the minimum exposure age for one bedrock sample is similar to that at Friendship Mountain (i.e., 44 ka). Our results indicate that the bedrock exposure in the Larsemann Hills and on the neighboring Bolingen Islands commenced obviously before the global LGM (i.e., 20–22 ka), and the bedrock erosion rates at the Antarctic coast areas may be obviously higher than in the interior land. © 2010, Wiley-Blackwell.
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    Using macromolecular neutron crystallography to study hydrogen atoms in the catalytic mechanism of the FADH cofactor in cholesterol oxidase
    (International Conference on Neutron Scattering, 2017-07-12) Golden, E; Yu, LJ; Meilleur, F; Blakeley, MP; Duff, AP; Karton, A; Vrielink, A
    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.