Vibrational assignment of the ultrafast infrared spectrum of the photoactivatable flavoprotein AppA

Allison Haigney, Andras Lukacs, Richard Brust, Rui Zhao, Michael Towrie, Gregory M. Greetham, Ian Clark, Boris Illarionov, Adelbert Bacher, Ryu-Ryun Kim, Markus Fischer, Stephen R. Meech, Peter J. Tonge

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)

Abstract

The blue light using flavin (BLUF) domain proteins, such as the transcriptional antirepressor AppA, are a novel class of photosensors that bind flavin noncovalently in order to sense and respond to high-intensity blue (450 nm) light. Importantly, the noncovalently bound flavin chromophore is unable to undergo large-scale structural change upon light absorption, and thus there is significant interest in understanding how the BLUF protein matrix senses and responds to flavin photoexcitation. Light absorption is proposed to result in alterations in the hydrogen-bonding network that surrounds the flavin chromophore on an ultrafast time scale, and the structural changes caused by photoexcitation are being probed by vibrational spectroscopy. Here we report ultrafast time-resolved infrared spectra of the AppA BLUF domain (AppABLUF) reconstituted with isotopes of FAD, specifically [U-13C17]-FAD, [xylene-13C8]-FAD, [U-15N4]-FAD, and [4-18O1]-FAD both in solution and bound to AppABLUF. This allows for unambiguous assignment of ground- and excited-state modes arising directly from the flavin. Studies of model compounds and DFT calculations of the ground-state vibrational spectra reveal the sensitivity of these modes to their environment, indicating they can be used as probes of structural dynamics.
Original languageEnglish
Pages (from-to)10722-10729
Number of pages8
JournalThe Journal of Physical Chemistry B
Volume116
Issue number35
DOIs
Publication statusPublished - 6 Sep 2012

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