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MO: Fachverband Molekülphysik
MO 8: Photochemistry
MO 8.5: Vortrag
Dienstag, 13. März 2012, 11:30–11:45, V38.02
Ultrafast dynamics of photolyzed carbon monoxide in the primary docking site of hemoglobin, FixLH and R220H FixLH — •Patrick Nuernberger1,2, Kevin F. Lee1, Adeline Bonvalet1, Latifa Bouzhir-Sima1, Jean-Christophe Lambry1, Ursula Liebl1, Manuel Joffre1, and Marten H. Vos1 — 1Laboratoire d’Optique et Biosciences, Ecole Polytechnique, CNRS, and INSERM U696, 91128 Palaiseau, France — 2Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
We report a mid-IR study of the ultrafast dynamics of CO in the docking site of the heme proteins hemoglobin, FixLH and the mutant R220H FixLH. We employ a recently developed chirped-pulse upconversion method that allows for simultaneous measurement of the absorption of both heme-bound and docked CO with high spectral resolution and sensitivity. The bacterial oxygen sensor FixLH displays marked differences in dynamic behavior upon ligand dissociation with respect to hemoglobin. We find that CO bound to the heme iron in FixL is tilted by ≈30∘ with respect to the heme normal, which contrasts to the situation in globins and in present FixLH-CO X-ray crystal structure models. This implies protein environment-induced strain on the ligand, which is possibly at the origin of a very rapid docking site population in a single conformation. Our observations likely explain the unusually low affinity of FixL for CO that is at the origin of the weak ligand discrimination between CO and O2.