Understanding the Electon Paramagnetic Resonance Parameters of Protein-Bound Glycyl Radicals

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• 作者：Sylwia Kacprzak ; Roman Reviakine ; Martin Kaupp
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：February 1, 2007
• 年：2007
• 卷：111
• 期：4
• 页码：820 - 831
• 全文大小：419K
• 年卷期：v.111,no.4(February 1, 2007)
• ISSN：1520-5207

文摘

The number of enzymes that require a glycyl-based radical for their function is growing. Here, we providesystematic quantum-chemical studies of spin-density distributions, electronic g-tensors, and hyperfine couplingsof various models of protein-bound glycyl radicals. Similarly to what is found in a companion paper onN-acetylglycyl, the small g-anisotropy for this delocalized, unsymmetrical system presents appreciablechallenges to state-of-the-art computational methodology. This pertains to the quality of structure optimization,as well as to the choice of the spin-orbit Hamiltonian and the gauge origin of the magnetic vector potential.Environmental effects due to hydrogen bonding are complicated and depend in a subtle fashion on the differentintramolecular hydrogen bonding for different conformations of the radical. Indeed, the conformation has thelargest overall effect on the computed g-tensors (less so on the hyperfine tensors). This is discussed in thecontext of different g-tensors obtained by recent high-field electron paramagnetic resonance (EPR)measurements for three different enzymes. On the basis of results of a parallel calibration study forN-acetylglycyl, it is suggested that the glycyl radical observed for E. coli anaerobic RNR may have a fullyextended conformation, which differs from those of the corresponding radicals in pyruvate formate-lyase orbenzylsuccinate synthase.