Stability of protein-bound glycyl radical: a density functional theory study

Density functional theory is used to study different models of the glycyl radical in proteins. The radical is characterized by means of the Cα–H bond strength, geometry, spin distribution, and hyperfine parameters. It is shown that, due to substituent effects from the peptide bond, the protein-bound glycyl radical is less stable than the nonprotein-bound one. This effect is of great importance for the biological function of the glycyl radical. The capto-dative resonance stabilization is confirmed, and new resonances are suggested to arise due to the peptide bond, resulting in further delocalization of the unpaired spin.