On the local structure of the glycyl radical in different enzymes

Abstract

Full hyperfine coupling tensors are computed for different geometric conformers of the glycyl radical, using gradient corrected Density Functional Theory (DFT) together with large basis sets (IGLO-III). Comparison is made with three enzymes in which the radical is present, namely Escherichia coli pyruvate formate lyase (PFL), Escherichia coli anaerobic ribonucleotide reductase (RNR) and bacteriophage T4 anaerobic RNR. The excellent agreement in hyperfine coupling constants between theory and experiment confirms again that the radical is a glycyl radical and that, although embedded in the protein, it maintains the planar gas phase structure in both E. coli PFL and E. coli RNR. In contrast to these two systems, we propose a non-planar structure for bacteriophage T4 anaerobic RNR, in order to explain the unusually high A_zz(¹³C_α) coupling (66 G) recently measured by Sjöberg et al.¹⁸