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Center for Nonlinear Studies |
The initial excitation energy transfer in photosynthesis is mediated by the light harvesting antenna complexes (LHC) associated with the photosystem I and II reaction centers. Non-photochemical quenching (NPQ) is a major pathway that reduces the radical oxidative damage to the photosynthetic apparatus under high light conditions. The LHC protein CP29, a pigment-protein complex, has been implicated the NPQ response which is triggered by acidification of thylakoid lumen. A pH induced conformational transition involving this protein leads to the NPQ response that involves the increase in zeaxanthin (carotenoid quencher) and reorganization of LHCII. We have conducted several microseconds molecular dynamics (MD) simulations of the CP29 complex in a thylakoid membrane mimic at full atomistic resolution. Our results suggest that protonation of different susceptible residues present in the lumenal interface leads to very subtle configurational changes in the transmembrane helices of the CP29 complex. Furthermore, water penetrates deeply into the thylakoid membrane. Consequently, several pH-sensitive residues, both proximal and distal to the chlorophylls, are susceptible to changes in protonation states upon decrease in lumenal pH. By considering long-time scale all-atom MD simulations of the CP29 complex in a thylakoid membrane, we have been able to show that that pH sensing is an acquired mechanism in CP29 that may trigger the NPQ process.
Host: Jeffrey Hyman