1 research outputs found
Raman Optical Activity Reveals Carotenoid Photoactivation Events in the Orange Carotenoid Protein in Solution
The
orange carotenoid protein (OCP) plays an important role in
photoprotection in cyanobacteria, which is achieved by the photoconversion
from the orange dark state (OCP<sup>O</sup>) to the red active state
(OCP<sup>R</sup>). Using Raman optical activity (ROA), we studied
the conformations of the carotenoid chromophore in the active sites
of OCP<sup>O</sup> and OCP<sup>R</sup>. This ROA measurement directly
observed the chromophore conformation of native OCP in solution, and
the measurement of OCP<sup>R</sup> first demonstrated the ROA spectroscopy
for the transient species. For OCP<sup>O</sup>, the spectral features
of ROA were mostly reproduced by the quantum chemical calculation
based on the crystal structure of the OCP. Within the spatial resolution
(∼2 Å), a slight modification of the polyene-chain distortion
improved the agreement between the observed and calculated ROA spectra.
While the crystal structure of OCP<sup>R</sup> is not available, the
ROA spectrum of OCP<sup>R</sup> was reproduced by using the crystal
structure of red carotenoid protein (RCP), an OCP<sup>R</sup> proxy.
The present results showed that the chromophore conformations in the
crystal structures of OCP and RCP hold true for OCP<sup>O</sup> and
OCP<sup>R</sup> in solution. Particularly, ROA spectroscopy of the
native OCP<sup>R</sup> provides a direct support for the 12 Ã…
translocation of chromophore in the photoactivation, which was proposed
by X-ray crystallography using RCP [R. L. Leverenz, M. Sutter, et
al. <i>Science</i> <b>2015</b>, 348, 1463–1466]