Dynamical and allosteric regulation of photoprotection in light harvesting complex II

The robustness of the terminal emitter site in major LHCII complexes controls xanthophyll function during photoprotection

“…19,48 In the thylakoids, regulation of light harvesting relies on the interplay between the protein PsbS, the xanthophyll cycle, lipids and involves ΔpH formation and membrane reorganisation events. 22,[55][56][57] Therefore, all in vitro setups come at a cost regarding the dynamical aspect of NPQ, as the above-mentioned factors are needed for the quick activation and de-activation of the quenching mechanism. However, despite being a very simplified model, the pigment architecture of LHCII and the signature of quencher formation are preserved in gel, making it a useful strategy to study the changes in energy equilibration pathways while avoiding the complexity of the thylakoid membrane.…”

“…20 It is likely that a gradual conformational change varies the orientation and coupling of chlorophylls and the L1 xanthophyll, enabling the formation of dissipative interactions. 57,63,85,86 The allosteric modulation by zeaxanthin and PsbS and the cooperative nature of the quenching switch grant the controlled modulation of the light harvesting function of LHCII in vivo. 22…”

Bridging Carotenoid-to-Bacteriochlorophyll Energy Transfer of Purple Bacteria LH2 With Temperature Variations: Insights From Conformational Changes

“…The N-terminus of α and β polypeptide helices possess high structural flexibility indicated by their B-factor values observed in crystallographic data ( Papiz et al, 2003 ). A recent study has shown that the structures near the terminus of these helices for other complexes in light harvesting system could be affected by temperature changes ( Li et al, 2020 ). Thus, in the present study, the residues near the N-terminus of α and β polypeptide helices were closely monitored during the course of the MD simulations ( Figure 3A ).…”

“…Exploring the mechanisms of temperature adaptation has a profound impact on understanding the energy transfer process of photosynthesis. Studies of higher plants showed that the temperature was one of the regulatory switches for light-harvesting complex of photosystem II (LHCII), which plays an essential role in their light energy harvesting process ( Li et al, 2020 ). Yet, such regulatory mechanisms, if existed, have not been thoroughly studied for LH2 in purple bacteria.…”

“…Furthermore, the increase of the temperature to 70°C led to the disappearances for the absorption peaks at both 800 and 850 nm and the appearance for a new and dominating absorption peak at 775 nm, which were caused by large-scale deformation of the protein indicated by the Circular dichroism (CD) spectroscopy measurements ( Ratsep et al, 2018 ). Many theoretical studies also showed that temperature could alter the conformations for proteins and surround pigment molecules in LH2, and, in turn, mediate the site energies and electronic couplings between pigment molecules, and eventually affect the light capture capability and energy transfer efficiencies of pigment molecules ( Cupellini et al, 2016 ; Li et al, 2020 ). Yet, the underlying mechanism of these regulations at the atomic level requires further elucidation.…”