Dynamics of Carbon Monoxide Photodissociation in Bradyrhizobium japonicum FixL Probed by Picosecond Midinfrared Spectroscopy

L. van Wilderen, J.M. Key, I.H.M. van Stokkum, R. van Grondelle, M.L. Groot

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

The FixL proteins are heme-based bacterial oxygen sensors, distinct from globins in structure and ligand binding properties. To better understand the dynamics of ligand dissociation and binding within the PAS domain fold of FixL, we have carried out picosecond visible pump-midinfrared probe spectroscopy on the isolated PAS domain of FixL from Bradyrhizobium japonicum. We employ the diatomic ligand CO as a probe of the ligand-dissociation pocket dynamics; upon photoexcitation with a visible laser pulse, CO is released and the infrared-active stretch frequency of the CO molecule changes, as it is very sensitive to interactions with the surrounding protein. The infrared absorption difference spectra indicate that the escape of photolyzed CO to solvent is preceded by transient docking within the protein in a manner similar to globins. A small-scale spectral change of the CO molecule on a picosecond time scale is likely due to changes in heme-protein conformation associated with cooling. A larger scale spectral evolution on a nanosecond time scale indicates a structural change in the protein, possibly related to changes in the β-strands associated with the transition from CO-bound to deoxy in BjFixLH (Key, J.; Srajer, V.; Pahl, R.; Moffat, K. Biochemistry 2007, 46, 4706). © 2009 American Chemical Society.
Original languageEnglish
Pages (from-to)3292-3297
JournalJournal of Physical Chemistry B
Volume113
Issue number11
DOIs
Publication statusPublished - 2009

Bibliographical note

Dynamics of Carbon Monoxide Photodissociation in Bradyrhizobium japonicum FixL Probed by Picosecond Midinfrared Spectroscopy

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