Nuclear inelastic scattering of heme proteins: from iron ligand vibrations to low energy protein modes

Abstract

The binding of the signal molecule nitric oxide (NO) to the NO transporter protein Nitrophorin 2 (NP2) from the bloodsucking insect Rhodnius prolixus has been characterized by Mossbauer spectroscopy as well as nuclear forward scattering (NFS) and nuclear inelastic scattering (NIS). A striking feature of the vibrational spectrum obtained from NP2-NO is a vibration at 594 cm − 1. This mode is assigned to a Fe-NO stretching mode via simulation of the NIS data by density functional theory (DFT) coupled with molecular mechanics (MM) methods. At frequencies below 100 cm − 1 collective motions like heme doming occur which could explain spectroscopic features observed by NIS at these low energies.