Protein and lipid dynamics in photosynthetic thylakoid membranes investigated by in-situ solid-state NMR

Abstract

Photosynthetic thylakoid membranes contain the protein machinery to convert sunlight in chemical energy and regulate this process in changing environmental conditions via interplay between lipid, protein and xanthophyll molecular constituents. This work addresses the molecular effects of zeaxanthin accumulation in thylakoids, which occurs in native systems under high light conditions through the conversion of the xanthophyll violaxanthin into zeaxanthin via the so called xanthophyll cycle. We applied biosynthetic isotope labeling and C solid-state NMR spectroscopy to simultaneously probe the conformational dynamics of protein, lipid and xanthophyll constituents of thylakoids isolated from wild type (cw15) and npq2 mutant of the green alga Chlamydomonas reinhardtii, that accumulates zeaxanthin constitutively. Results show differential dynamics of wild type and npq2 thylakoids. Ordered-phase lipids have reduced mobility and mobile-phase lipids have enlarged dynamics in npq2 membranes, together spanning a broader dynamical range. The fraction of ordered lipids is much larger than the fraction of mobile lipids, which explains why zeaxanthin appears to cause overall reduction of thylakoid membrane fluidity. In addition to the ordered lipids, also the xanthophylls and a subset of protein sites in npq2 thylakoids have reduced conformational dynamics. Our work demonstrates the applicability of solid-state NMR spectroscopy for obtaining a microscopic picture of different membrane constituents simultaneously, inside native, heterogeneous membranes.

Conformational dynamics of Light-Harvesting Complex II in a native membrane environment

“…C: chemical structure of Chl with the assigned carbon atom types colored in green.The lipid signals in the thylakoid spectra provide a unique molecular picture of lipid dynamics inside the thylakoid membrane. Lipid signals are detected both in the J-based and in the dipolar-based CC spectrum, indicating that the thylakoid membrane contains mobile lipids with strong dynamics and low segmental order, as well as immobilized lipids with low dynamics, which notion is in agreement with our previous work(58). In the previous work, we tentatively assigned lipid signals from 1D 13 C MAS NMR (59).…”

A proteoliposome-based system reveals how lipids control photosynthetic light harvesting

“…In this respect, the xanthophyll zeaxanthin (zea) is interesting. The presence of zea in the lipid bilayer increases membrane order and rigidity (59,60) that is known to enhance the lateral membrane pressure in hydrophobic membrane regions (13). Zea is converted from violaxanthin by the xanthophyll cycle and promotes qE formation (61,62).…”

Diadinoxanthin de‐epoxidation as important factor in the short‐term stabilization of diatom photosynthetic membranes exposed to different temperatures

“…They have to be regulated by precise and fast reacting mechanisms, in order to adapt to numerous changes of environmental factors such as light and temperature fluctuations. Regulation of the physical properties of thylakoid membranes often requires the interaction of different membrane components, such as lipids, pigments, and proteins (Chegeni et al, 2016;Cruz et al, 2005;Nowicka & Kruk, 2016;Strzałka & Machowicz, 1984;van Eerden, de Jong, de Vries, Wassenaar, & Marrink, 2015). Among the pigments, the most important role is played by the carotenoids, which influence the motional freedom of lipid alkyl chains, thereby changing the physical properties of the membranes (Gruszecki & Strzałka, 2005).…”