Összes szerző

Biswas Avratanu

az alábbi absztraktok szerzői között szerepel:

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

Lambrev Petar
Light energy harvesting by photosystem I in cyanobacterial cells

Aug 30 - szerda

15:30 – 17:00

II. Poszterszekció

P45

Light energy harvesting by photosystem I in cyanobacterial cells

Petar Lambrev¹, Parveen Akhtar¹, Avratanu Biswas¹, Ivo van Stokkum²

¹ Biological Research Centre, Szeged, Institute of Plant Biology

² Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands

Photosystem I (PSI) is a crucial component of the light-dependent reactions of oxygenic photosynthesis occurring in cyanobacteria, algae and plants. It is a multi-subunit pigment-protein complex binding more than a hundred pigment – chlorophylls (Chls) and carotenoids, as well as cofactors carrying out photoinduced electron transport with a quantum yield of near unity. Whereas PSI in plants and eukaryotic algae is attached to peripheral membrane-intrinsic light-harvesting complexes, cyanobacteria utilize the membrane extrinsic phycobilisomes (PBS) as the main light-harvesting antenna complex¹. While the structural and energetic interaction between the PBS and photosystem II (PSII) is well established, less is known about the connectivity of PBS and PSI and the ability of the PBS to transfer energy directly to PSI is debated. We investigated the pathways and dynamics of energy transfer from PBS to the photosystems in Synechocystis sp. PCC 6803. The excitation kinetics of PBS and PSI were followed by picosecond time-resolved fluorescence spectroscopy in the wild-type strain and in a mutant devoid of PSII². We found that PBS are capable of directly transferring energy to PSI in the PSII-deficient mutant, in a time scale of about 20 ps at room temperature. Based on an earlier model of energy transfer in Synechocystis sp. PCC 6803³ and simultaneous fitting to the measured data of isolated complexes and intact cells, a detailed model of energy transfer between different PBS, PSI and PSII chromophore groups was obtained.

Many cyanobacterial species, when exposed to iron limitation conditions, produce a specialized pigment-protein complex, IsiA, that is known to associate into rings around PSI⁴. The physiological function of IsiA is not fully understood. In isolated PSI-IsiA complexes IsiA efficiently transfers absorbed photon energy to the PSI core⁵, which can extend the absorption cross-section of the photosystem and help reduce the number of iron-rich PSI core complexes in the cells. However, IsiA has also been proposed to have a photoprotective, energy-dissipating role or to serve as a Chl depot⁶. To find more about the light-harvesting role of IsiA in vivo, we followed the cellular content of IsiA in cells of Synechocystis sp. PCC 6803 under iron limitation and investigated the energy transfer from IsiA to PSI by time-resolved spectroscopy. IsiA formed PSI-IsiA supercomplexes in vivo having similar energy transfer characteristics as isolated supercomplexes – confirming the primary role of IsiA as an accessory light-harvesting antenna to PSI. However, a significant fraction (40%) remained unconnected to PSI, supporting the notion of a dual functional role of IsiA. Moreover, we found that Synechocystis mutants containing only monomeric PSI contained far fewer IsiA units per PSI compared to the wild-type strain. We conclude that the trimeric organization of PSI in wild-type Synechocystishas role both in the accumulation and the energy transfer capabilities of IsiA under iron stress.

References

1. Blankenship, R. E., Molecular mechanisms of photosynthesis. John Wiley & Sons: 2021.

2. Bittersmann, E.; Vermaas, W., Fluorescence lifetime studies of cyanobacterial photosystem II mutants. Biochim. Biophys. Acta 1991, 1098 (1), 105–116.

3. van Stokkum, I. H.; Gwizdala, M.; Tian, L.; Snellenburg, J. J.; van Grondelle, R.; van Amerongen, H.; Berera, R., A functional compartmental model of the Synechocystis PCC 6803 phycobilisome. Photosynth. Res. 2018, 135 (1-3), 87–102.

4. Toporik, H.; Li, J.; Williams, D.; Chiu, P.-L.; Mazor, Y., The structure of the stress-induced photosystem I–IsiA antenna supercomplex. Nat. Struct. Mol. Biol. 2019, 26 (6), 443–449.

5. Andrizhiyevskaya, E. G.; Frolov, D.; van Grondelle, R.; Dekker, J. P., Energy transfer and trapping in the photosystem I complex of Synechococcus PCC 7942 and in its supercomplex with IsiA. Biochim. Biophys. Acta 2004, 1656 (2–3), 104–113.

6. Jia, A.; Zheng, Y.; Chen, H.; Wang, Q., Regulation and functional complexity of the chlorophyll-binding protein IsiA. Frontiers in Microbiology 2021, 12, 774107.