Electronic excited states of the CP29 antenna complex of green plants: a model based on exciton calculations
We have suggested a model for the electronic excited states of the minor plant antenna, CP29, by incorporating a considerable part of the current information offered by structure determination, site-directed mutagenesis, and spectroscopy in the modeling. We have assumed that the electronic excited states of the complex have been decided by the chlorophyll-chlorophyll (Chl) and Chl-protein interactions and have modeled the Coulombic interaction between a pair of Chls in the point-dipole approximation and the Chl-protein interactions are treated as empirical fit parameters. We have suggested the Qy dipole moment orientations and the site energies for all the chlorophylls in the complex through a simultaneous simulation of the absorption and linear dichroism spectra. The assignments proposed have been discussed to yield a satisfactory reproduction of all prominent features of the absorption, linear and circular dichroism spectra as well as the key spectral and temporal characteristics of the energy transfer processes among the chlorophylls. The orientations and the spectral assignments obtained by relatively simple exciton calculations have been necessary to provide a good point of departure for more detailed treatments of structure-function relationship in CP29. Moreover, it has been discussed that the CP29 model suggested can guide the studies for a better understanding of the structure-function relationship in the major plant antenna, LHCII.