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Böde Kinga
Lipid polymorphism of Photosystem II membranes – evidence of the role of isotropic lipid phase in membrane fusions

Aug 30 - szerda

08:30 – 08:45

Membránok és membránfehérjék biofizikája

E19

Lipid polymorphism of photosystem II membranes – evidence of the role of isotropic lipid phase in membrane fusions

Kinga Böde^1,2,3, Ottó Zsíros¹, Ondřej Dlouhý³, Uroš Javornik⁴, Avratanu Biswas^1,2, Primož Šket⁴, Janez Plavec^4,5,6, Vladimír Špunda³, Petar H Lambrev¹, Bettina Ughy¹ and Győző Garab^1,3

¹Institute of Plant Biology, Biological Research Centre, Szeged, Hungary

²Doctoral School of Biology, University of Szeged, Szeged, Hungary

³Department of Biophysics, University of Ostrava, Ostrava, Czech Republic

⁴National Institute of Chemistry, Ljubljana, Slovenia

⁵EN-FIST Center of Excellence, Ljubljana, Slovenia

⁶Faculty of Chemistry and Chemical Technology, University of Ljubljana, Ljubljana, Slovenia

Plant thylakoid membranes (TMs), in addition to the bilayer (or lamellar, L) phase, contain at least two isotropic (I) lipid phases and an inverted hexagonal (H_II) phase. The non-bilayer propensity of bulk TM lipids has been proposed to safe-guard the lipid homeostasis of TMs; further, an I phase has been shown to arise from VDE:lipid assemblies (VDE is a luminal photoprotective enzyme) [1]. Effects of proteases and lipases on the lipid polymorphism of TMs have revealed that the H_II phase originates from lipids encapsulating stroma-side proteins and that the non-bilayer phases are to be found in domains outside the protein-rich regions of TM vesicles; an I phase is proposed to be involved in the fusion of membranes and thus in the self-assembly of the TM network [2].

The aim of the present study was to test the hypothesis on the role of I phase in the membrane fusion.

We capitalize on the fact that wheat-germ lipase (WGL) selectively eliminates the ³¹P-NMR-spectroscopy detectable I phases while it exerts no effect on the L and H_II phases and does not perturb the structure and function of the photosynthetic machinery [2].

Our data show that (i) Photosystem II (BBY) subchloroplast particles, compared to intact TMs, display weaker L and I phases and no H_II phase – in accordance with the diminished lipid content of these particles and the absence of stroma TM; (ii) similar to intact TMs, WGL has no effect on the molecular organization and functional activity of BBY particles but (iii) eliminates their I phase; and (iv) parallel with the diminishment of the I phase, it disintegrates the large (>10 μm diameter) sheets of the BBY membranes, which are composed of stacked membrane pairs of granum thylakoids of ~500 nm diameter. These data provide evidence on the involvement of I phase in the lateral fusion of stacked Photosystem II membranes.

References

[1] Garab G. et al. 2022 Progr Lipid Res; [2] Dlouhý et al. 2022 Cells