Network modeling of chlorophyll excitation transfer rates in cyanobacterial photosystem I in the dipolar coupling approximation


The flow of excitation energy in photosystems can be described by the energy funnel model, where excitations from the higher-energy antenna pigments are funneled toward the lower-energy reaction-center chlorophylls, eventually reaching the P700 where charge separation takes place. Thus, energy transfer flow between chlorophylls in a photosystem can be modeled as a network. In this study, a network of the energy flow between individual chlorophyll nodes in cyanobacterial photosystem I (from Synechococcus elongatus) is constructed. The nodes of the graph are the chlorophyll molecules, which are all the chlorophyll a type. The edge weights are the quantum-mechanical transfer rates constructed under the Förster dipole-dipole approximation. From the network, chlorophylls serving as excitation sinks and sources, as well as "central" chlorophylls from a betweenness-centrality-based metric of antenna-to-P700 energy flow, were identified. Characterization of these crucial nodes can be extended to other complex photosynthetic units, as these nodes could play a critical role in the network functioning of photosynthetic energy transfer.