TY - JOUR
T1 - Two-Step Structural Changes in Orange Carotenoid Protein Photoactivation Revealed by Time-Resolved Fourier Transform Infrared Spectroscopy
AU - Mezzetti, Alberto
AU - Alexandre, Maxime
AU - Thurotte, Adrien
AU - Wilson, Adjelé
AU - Gwizdala, Michal
AU - Kirilovsky, Diana
PY - 2019/4/18
Y1 - 2019/4/18
N2 -
The orange carotenoid protein (OCP), which is essential in cyanobacterial photoprotection, is the first photoactive protein containing a carotenoid as an active chromophore. Static and time-resolved Fourier transform infrared (FTIR) difference spectroscopy under continuous illumination at different temperatures was applied to investigate its photoactivation mechanism. Here, we demonstrate that in the OCP, the photo-induced conformational change involves at least two different steps, both in the second timescale at 277 K. Each step involves partial reorganization of α-helix domains. At early illumination times, the disappearance of a nonsolvent-exposed α-helix (negative 1651 cm
-1
band) is observed. At longer times, a 1644 cm
-1
negative band starts to bleach, showing the disappearance of a solvent-exposed α-helix, either the N-terminal extension and/or the C-terminal tail. A kinetic analysis clearly shows that these two events are asynchronous. Minor modifications in the overall FTIR difference spectra confirm that the global protein conformational change consists of - at least - two asynchronous contributions. Comparison of spectra recorded in H
2
O and D
2
O suggests that internal water molecules may contribute to the photoactivation mechanism.
AB -
The orange carotenoid protein (OCP), which is essential in cyanobacterial photoprotection, is the first photoactive protein containing a carotenoid as an active chromophore. Static and time-resolved Fourier transform infrared (FTIR) difference spectroscopy under continuous illumination at different temperatures was applied to investigate its photoactivation mechanism. Here, we demonstrate that in the OCP, the photo-induced conformational change involves at least two different steps, both in the second timescale at 277 K. Each step involves partial reorganization of α-helix domains. At early illumination times, the disappearance of a nonsolvent-exposed α-helix (negative 1651 cm
-1
band) is observed. At longer times, a 1644 cm
-1
negative band starts to bleach, showing the disappearance of a solvent-exposed α-helix, either the N-terminal extension and/or the C-terminal tail. A kinetic analysis clearly shows that these two events are asynchronous. Minor modifications in the overall FTIR difference spectra confirm that the global protein conformational change consists of - at least - two asynchronous contributions. Comparison of spectra recorded in H
2
O and D
2
O suggests that internal water molecules may contribute to the photoactivation mechanism.
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U2 - 10.1021/acs.jpcb.9b01242
DO - 10.1021/acs.jpcb.9b01242
M3 - Article
C2 - 30895789
AN - SCOPUS:85064344760
VL - 123
SP - 3259
EP - 3266
JO - The Journal of Physical Chemistry B
JF - The Journal of Physical Chemistry B
SN - 1520-6106
IS - 15
ER -
