Orange Carotenoid Protein Absorption Spectra Simulation Using the Differential Evolution Algorithm

Abstract

Linear optical response of the orange carotenoid protein (OCP) and its mutants was successfully simulated by applying the Differential evolution (DE) algorithm. OCP is a pigment-protein complex, which plays an important role in non-photochemical quenching of excitation energy in photosynthetic light-harvesting complexes in cyanobacteria. It contains a single carotenoid pigment molecule surrounded by protein matrix. This pigment is entirely responsible for OCP absorption in the region of 350–600 nm. To calculate the OCP absorption spectra, we used the Multimode Brownian oscillator model considering four high vibronic modes (\( \upnu_{1} \), \( \upnu_{2} \), \( \upnu_{3} \) and \( \upnu_{4} \)) and one low frequency mode. The frequencies of these modes were estimated from the OCP Raman spectra; whereas the Huang-Rhys factors alongside the carotenoid electronic transition and the FWHM of inhomogeneous broadening and the low frequency mode were fitted by DE. It was show that characteristic features of OCP absorption spectra can be explained by mutual variations of Huang-Rhys factors of \( \upnu_{1} \) and \( \upnu_{2} \) that is corresponded to the in-phase stretching of C = C and C-C bonds.