Optimization and evolution of light harvesting in photosynthesis: the role of antenna chlorophyll conserved between photosystem II and photosystem I.
The efficiency of oxygenic photosynthesis depends on the presence of core antenna chlorophyll closely associated with the photochemical reaction centers of both photosystem II (PSII) and photosystem I (PSI). Although the number and overall arrangement of these chlorophylls in PSII and PSI differ, structural comparison reveals a cluster of 26 conserved chlorophylls in nearly identical positions and orientations. To explore the role of these conserved chlorophylls within PSII and PSI we studied the influence of their orientation on the efficiency of photochemistry in computer simulations. We found that the native orientations of the conserved chlorophylls were not optimal for light harvesting in either photosystem. However, PSII and PSI each contain two highly orientationally optimized antenna chlorophylls, located close to their respective reaction centers, in positions unique to each photosystem. In both photosystems the orientation of these optimized bridging chlorophylls had a much larger impact on photochemical efficiency than the orientation of any of the conserved chlorophylls. The differential optimization of antenna chlorophyll is discussed in the context of competing selection pressures for the evolution of light harvesting in photosynthesis.
Vasil'ev
Sergej
S
Department of Biological Sciences, Brock University, St. Catharines, Ontario, L2S 3A1, Canada. svassili@brocku.ca
Bruce
Doug
D
D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D003198:Computer Simulation; D019143:Evolution, Molecular; D008027:Light; D008954:Models, Biological; D010777:Photochemistry; D010788:Photosynthesis / Q000502:physiology*; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology
D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll