Relationship between protein structural fluctuations and rebinding dynamics in ferric haem nitrosyls
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Updated: Jun 6, 2026

NMR 15N Relaxation Experiments for the Investigation of Picosecond to Nanoseconds Structural Dynamics of Proteins
Published on: November 1, 2024
Neil T Hunt1, Gregory M Greetham, Michael Towrie
1Department of Physics, University of Strathclyde, Glasgow, Scotland, UK.
Abstract:
The interaction of nitric oxide (NO) with haem proteins is widespread in biology. In the current paper, we present the first ultrafast 2D-IR (two-dimensional infrared) spectroscopic analysis of haem nitrosylation, which has been combined with time-resolved IR pump-probe studies to investigate the relationship between equilibrium vibrational dynamics of the haem environment and ligand rebinding behaviour following photolysis of NO from the Fe(III)-NO site. Studies of two haem proteins, Mb (myoglobin) and Cc (cytochrome c), which play different physiological roles, reveal marked contrasts in the ultrafast fluctuations of the protein pockets containing the haem, showing that the Mb pocket is somewhat more flexible than that of Cc. This correlates strongly with slower observed photolysis rebinding kinetics of Mb-NO compared with Cc-NO, and indicates a direct link between ultrafast fluctuations and biological functionality. Furthermore, this indicates the validity of linear response theories in relation to protein ligand binding. Finally, 2D-IR shows that Cc-NO displays two distinct structural sub-sites at room temperature that do not exchange on the timescales accessible via the NO vibrational lifetime.
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