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Structural Interpretation of the Large Slowdown of Water Dynamics at Stacked Phospholipid Membranes for Decreasing Hydration Level: All-Atom Molecular Dynamics.

ABSTRACT: Hydration water determines the stability and function of phospholipid membranes as well as the interaction of membranes with other molecules. Experiments and simulations have shown that water dynamics slows down dramatically as the hydration decreases, suggesting that the interfacial water that dominates the average dynamics at low hydration is slower than water away from the membrane. Here, based on all-atom molecular dynamics simulations, we provide an interpretation of the slowdown of interfacial water in terms of the structure and dynamics of water-water and water-lipid hydrogen bonds (HBs). We calculate the rotational and translational slowdown of the dynamics of water confined in stacked phospholipid membranes at different levels of hydration, from completely hydrated to poorly hydrated membranes. For all hydrations, we analyze the distribution of HBs and find that water-lipids HBs last longer than water-water HBs and that at low hydration most of the water is in the interior of the membrane. We also show that water-water HBs become more persistent as the hydration is lowered. We attribute this effect (i) to HBs between water molecules that form, in turn, persistent HBs with lipids; (ii) to the hindering of the H-bonding switching between water molecules due to the lower water density at the interface; and (iii) to the higher probability of water-lipid HBs as the hydration decreases. Our interpretation of the large dynamic slowdown in water under dehydration is potentially relevant in understanding membrane biophysics at different hydration levels.

SUBMITTER: Calero C

PROVIDER: S-EPMC5503093 | biostudies-other | 2016 Apr

REPOSITORIES: biostudies-other

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Project description:Highlights • Combined spin-label EPR and MAS NMR to characterize thylakoid membrane dynamics.• Assessment of dynamics of bulk, annular and structural lipids and proteins.• Thylakoid unstacking increases lipid ps-ns dynamics at different membrane depths.• Thylakoid unstacking increases ms-ms dynamics of protein helices. Chloroplast thylakoid membranes in plants and green algae form 3D architectures of stacked granal membranes interconnected by unstacked stroma lamellae. They undergo dynamic structural changes as a response to changing light conditions that involve grana unstacking and lateral supramolecular reorganization of the integral membrane protein complexes. We assessed the dynamics of thylakoid membrane components and addressed how they are affected by thylakoid unstacking, which has consequences for protein mobility and the diffusion of small electron carriers. By a combined nuclear and electron paramagnetic-resonance approach the dynamics of thylakoid lipids was assessed in stacked and cation-depletion induced unstacked thylakoids of Chlamydomonas (C.) reinhardtii. We could distinguish between structural, bulk and annular lipids and determine membrane fluidity at two membrane depths: close to the lipid headgroups and in the lipid bilayer center. Thylakoid unstacking significantly increased the dynamics of bulk and annular lipids in both areas and increased the dynamics of protein helices. The unstacking process was associated with membrane reorganization and loss of long-range ordered Photosystem II- Light-Harvesting Complex II (PSII-LHCII) complexes. The fluorescence lifetime characteristics associated with membrane unstacking are similar to those associated with state transitions in intact C. reinhardtii cells. Our findings could be relevant for understanding the structural and functional implications of thylakoid unstacking that is suggested to take place during several light-induced processes, such as state transitions, photoacclimation, photoinhibition and PSII repair.

Dataset Information

Structural Interpretation of the Large Slowdown of Water Dynamics at Stacked Phospholipid Membranes for Decreasing Hydration Level: All-Atom Molecular Dynamics.

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