Prediction of Thylakoid Lipid Binding Sites on Photosystem II

Floris J Van Eerden,Manuel N Melo,Pim W.J.M Frederix,Siewert J Marrink

doi:10.1016/j.bpj.2017.09.039

Floris J Van Eerden, Manuel N Melo + Show 2 more

Open Access

https://doi.org/10.1016/j.bpj.2017.09.039

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Abstract

The thylakoid membrane has a unique lipid composition, consisting mostly of galactolipids. These thylakoid lipids have important roles in photosynthesis. Here, we investigate to what extent these lipids bind specifically to the Photosystem II complex. To this end, we performed coarse-grain MD simulations of the Photosystem II complex embedded in a thylakoid membrane with realistic composition. Based on >85 μs simulation time, we find that monogalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol lipids are enriched in the annular shell around the protein, and form distinct binding sites. From the analysis of residue contacts, we conclude that electrostatic interactions play an important role in stabilizing these binding sites. Furthermore, we find that chlorophyll a has a prevalent role in the coordination of the lipids. In addition, we observe lipids to diffuse in and out of the plastoquinone exchange cavities, allowing exchange of cocrystallized lipids with the bulk membrane and suggesting a more open nature of the plastoquinone exchange cavity. Together, our data provide a wealth of information on protein-lipid interactions for a key protein in photosynthesis.

Highlights

PSII is a major player of the photosynthetic machinery, the process by which light is converted into chemical energy in plants, algae, and cyanobacteria
PSII is located in the thylakoid membrane, together with photosystem I (PSI), cytochrome b6f complex, and ATP synthase, the other major proteins involved in photosynthesis
We previously reported on the overall dynamics of the cyanobacterial PSII complex including all of its cofactors [64] and on the exchange of the electron carriers plastoquinone and plastoquinol [65]

Summary

Introduction

PSII is a major player of the photosynthetic machinery, the process by which light is converted into chemical energy in plants, algae, and cyanobacteria. PSII is located in the thylakoid membrane, together with photosystem I (PSI), cytochrome b6f complex, and ATP synthase, the other major proteins involved in photosynthesis. The thylakoid membrane is atypical as it has a rather unusual composition, containing mainly galactolipids instead of the more common phospholipids. The predominant galactolipids found in the thylakoid membranes of higher plants and cyanobacteria are digalactosyldiacylglycerol (DGDG), monogalactosyldiacylglycerol (MGDG), and sulfoquinovosyldiacylglycerol (SQDG), together with phosphatidylglycerol (PG) [4,5]. The composition of the thylakoid membrane is conserved in evolution [5], indicating the importance of the galactolipids for photosynthesis. Experiments show that the lipid composition influences the dimerization state of the protein and the attachment of the inner antenna proteins, which are important for the electron transport within PSII [6]

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