Mononitrosyl and dinitrosyl iron species, such as {FeNO}7, {FeNO}8 and {Fe(NO)2}9, have been proposed to play pivotal roles in the nitrosylation processes of nonheme iron centers in biological systems. Despite their importance, it has been difficult to capture and characterize them in the same scaffold of either native enzymes or their synthetic analogs using redox reagents compatible with biomolecules under physiological conditions. Our experimental collaborators recently studied the stepwise nitrosylation of a mononuclear nonheme iron site in an engineered azurin under such a condition. Some general features of the involved nitrosyl species were characterized and/or hinted from the analysis of a number of spectroscopic data. But there is no experimental atomic level structural information. To confirm such experimental findings and reveal the actual molecular structures of these species, a comprehensive DFT investigation was done to compare different possible structures with different possible spin states. The entire pathway of the nitrosylation process, from Fe(II) via {FeNO}7 and {FeNO}8 to {Fe(NO)2}9, has been elucidated for the first time in the same protein scaffold active site. This computational study gave excellent predictions of available experimental Mössbauer data with the average errors of only 0.06 and 0.18 mm/s for isomer shifts and quadrupole splittings respectively. The predicted vibrational spectroscopic data of these species are also accurate with ~1% error. These results enhance the understanding of dinitrosyl iron complexes formation process, which may shed light on the physiological roles of nitric oxide signaling mediated by nonheme iron proteins.

All species involved in the stepwise nitrosylation of the nonheme iron site in an engineered azurin

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.