Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 104, Issue 36, Pages 14243-14248Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0607758104
Keywords
ligand binding; myoglobin; chemical exchange; infrared spectroscopy
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2D-IR exchange spectroscopy has been introduced recently to map chemical exchange networks in equilibrium with subpicosecond time resolution. Here, we demonstrate the generalization of 2D-IR exchange spectroscopy to nonequilibrium systems and its application to map light-triggered migration of ligands between different sites in a protein. Within picoseconds after a photodissociating laser pulse, carbon monoxide ligands relocate from their binding site A at the heme prosthetic group of myoglobin to a primary docking site B in the distal heme pocket. Multiple CO stretching bands are observed for the CO ligand in sites A and B, indicating that several distinct conformational substates of the myoglobin: ligand complex coexist in solution. Exchange cross-peaks between the bands associated with sub-states of heme-bound CO and photodissociated CO in the primary docking site reveal the substate connectivity at physiological temperature.
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