Abstract
Photosynthesis is common in nature, converting sunlight energy into proton motive force and reducing power. The increased spectral range absorption of light exerted by pigments (i.e. chlorophylls, Chls) within Light Harvesting Complexes (LHCs) proves an important advantage under low light conditions. However, in the exposure to excess light, oxidative damages and ultimately cell death can occur. A down-regulatory mechanism, thus, has been evolved (non-photochemical quenching, NPQ). The mechanistic details of its major component (qE) are missing at the atomic scale. The research herein, initiates on solid evidence from the current NPQ state of the art, and reveals a detailed atomistic view by large scale Molecular Dynamics, Metadynamics and ab initio Simulations. The results demonstrate a complete picture of an elaborate common molecular design. All probed antenna proteins (major LHCII from spinach-pea, CP29 from spinach) show striking plasticity in helix-D, under NPQ conditions. This induces changes in Qy bands in excitation and absorption spectra of the near-by pigment pair (Chl613-614) that could emerge as a new quenching site. Zeaxanthin enhances this plasticity (and possibly the quenching) even at milder NPQ conditions.
Highlights
Photosystem II (PSII) is one of the most important biochemical nanomachines in nature and part of the photosynthetic apparatus of higher plants
It is well established that the energies and quenching dynamics of the pigment excited states within LHCII are regulated by pigment-protein interactions
What could be the cascade of events that leads from the well-established lumen acidification that triggers qE, to the obscure protein conformational changes and to the quenching site(s) and dynamics ? Our working hypothesis is that under different lumen perturbations (ΔpH and ΔΨ gradients), the active player (LHCs) domains related to Non-Photochemical Quenching (NPQ) will exert high flexibility, or will assume distinct structures upon the binding of Zea, where the pigment-pigment, or protein-pigment interactions are altered
Summary
Photosystem II (PSII) is one of the most important biochemical nanomachines in nature and part of the photosynthetic apparatus of higher plants. Our working hypothesis is that under different lumen perturbations (ΔpH and ΔΨ gradients), the active player (LHCs) domains related to NPQ will exert high flexibility, or will assume distinct structures upon the binding of Zea, where the pigment-pigment, or protein-pigment interactions are altered. Large scale all-atom Classical Molecular Dynamics (CMD), Metadynamics and full Quantum (ab initio) simulations are employed as powerful tools[16, 28,29,30,31,32], to give insight into the LHCs response under ΔpH − ΔΨ5 and the Vio−Zea conversion[6], in terms of induced conformational changes that can be associated with affected quenching sites. For further details refer to the Materials and Methods Section and the Supplementary Information (SI)
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