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. 2021 Jun 13:1:100015.
doi: 10.1016/j.bbadva.2021.100015. eCollection 2021.

Lipid and protein dynamics of stacked and cation-depletion induced unstacked thylakoid membranes

Faezeh Nami  1 , Lijin Tian  1 , Martina Huber  2 , Roberta Croce  3 , Anjali Pandit  1
Affiliations

Lipid and protein dynamics of stacked and cation-depletion induced unstacked thylakoid membranes

Faezeh Nami et al. BBA Adv. .

Abstract

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.

Keywords: Chlamydomonas reinhardtii; Dynamic spectral-editing NMR; Membrane fluidity; Photosynthesis; Spin-label EPR; Thylakoid plasticity.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig 1
Fig. 1
Arrangement of bulk lipids (pink), annular lipids (green) around a protein complex (blue) and non-annular lipids (yellow) within a multi-subunit protein complex.
Fig 2
Fig. 2
CD spectra of C. reinhardtii cells (black), stacked (red) and unstacked (blue) thylakoid membrane at 20°C. All samples are in 25 mM Hepes buffer, pH 7.5 plus 5 mM Mg2+ for the stacked membrane and 10% Ficoll for the cells.
Fig 3
Fig. 3
77 K steady-state fluorescence spectra of stacked (black) and unstacked (red) thylakoid membranes upon 400 nm excitation. The spectra are normalized at 683 nm.
Fig 4
Fig. 4
Time-resolved spectroscopy. DAS of stacked (solid) and unstacked thylakoid membranes (dot) upon 400 nm excitation. To simplify the analysis, lifetimes of two samples were forced to be identical during fitting and indicated in the Fig.. DAS were normalized to their time zero emission for direct comparison between two samples.
Fig 5
Fig. 5
Overlaid DP (black), CP (red) and INEPT (blue) 13C NMR spectra of stacked thylakoid membranes recorded at 10°C.
Fig 6
Fig. 6
Overlaid DP, CP, INEPT 13C NMR spectra of stacked (black) and unstacked (red) thylakoid membranes recorded at 10°C. The blue spectra show the difference spectrum of stacked minus unstacked. (A) DP, (B) CP and (C) INEPT.
Fig 7
Fig. 7
Experimental and simulated EPR spectra recorded at 19°C of 16-SASL in solution (A) and in stacked (B) and unstacked (C) membranes, and of 5-SASL in stacked (D) and unstacked (E) membranes. Experimental spectra are shown in black and the simulated spectra are overlaid in red (total spectrum), blue (the immobile component) and green (mobile component).
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