Összes szerző

Garab Győző

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 Böde1,2,3, Ottó Zsíros1, Ondřej Dlouhý3, Uroš Javornik4, Avratanu Biswas1,2, Primož Šket4, Janez Plavec4,5,6, Vladimír Špunda3, Petar H Lambrev1, Bettina Ughy1 and Győző Garab1,3

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 (HII) 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 HII 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 HII 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 HII 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

Garab Győző
The fascinating world of photosynthesis – best playground for biophysicists

Aug 28 - hétfő

18:00 – 18:40

Plenáris ülés

PE02

The fascinating world of photosynthesis – best playground for biophysicists

Győző Garab1,2

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

2Department of Biophysics, University of Ostrava, Ostrava, Czech Republic

In the 1970s scientists might have thought, paraphrasing De Gaulle, that ‘biology is too serious a matter to be left to biologists’. Probably this view justified my employment in 1971, a physicist with fresh diplom, in the Laboratory of Photosynthesis of the BRC. Certainly, photosynthesis research demands teams with multidisciplinary approach and offers important mind-boggling questions. With the treasured support from my students and colleagues I had a few ‘pet’ topics of this kind; here, I’ll dwell on two of them.

Photosystem II (PSII) uses light energy to oxidize water, providing us with an oxygenic atmosphere; by this means, it is the ultimate source of virtually all reducing equivalents in the Biosphere. Its activity is routinely monitored by recording the variable chlorophyll-a fluorescence (ChlF). The ‘mainstream’ interpretation of ChlF, which has never been free of controversies, is based on the 1963 two-state model (PSIIO, open and PSIIC closed). We revealed the existence of PSIIL, the light-adapted closed state, with stabilized charges compared to PSIIC; and showed that the physical mechanism of ChlF must be laid on new grounds, in which intense steady-state and transient local electric fields and dielectric relaxation processes and protein memory effects play key roles.

The Fluid-Mosaic Model (FMM) of biological membranes – with the bulk lipid molecules organized into bilayer – provides a framework for the photosynthetic generation of proton motive force and its chemiosmotic utilization for ATP synthesis. However, FMM does not take into account that the major lipid species of thylakoid membranes (TMs) is non-bilayer lipid, and allows no room for the thoroughly documented non-bilayer lipid phases in TMs. DEM, the Dynamic Exchange Model, an extension of FMM, explains the presently available data on the basic features of the highly organized, intervowen vesicular TM system and its plasticity; DEM appears to apply also on the inner mitochondrial membranes.

Magyar Melinda
Rate-limiting steps in the dark-to-light transition of photosystem II: Dependence on the temperature and the lipidic environment of the reaction center

Aug 31 - csütörtök

10:45 – 11:00

Bioenergetika és fotobiofizika

E41

Rate-limiting steps in the dark-to-light transition of photosystem II: Dependence on the temperature and the lipidic environment of the reaction center

Melinda Magyar1, Gábor Sipka1, Parveen Akhtar1, Guangye Han2, Petar H. Lambrev1, Jian-Ren Shen2,3 and Győző Garab1,4

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

2Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China

3Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan

4Faculty of Science, University of Ostrava, Ostrava, Czech Republic

Photosystem II (PSII) is the redox-active pigment–protein complex embedded in the thylakoid membrane (TM) that catalyzes the oxidation of water and the reduction of plastoquinone. We performed single-turnover saturating flash-induced (STSF) variable chlorophyll-a fluorescence transient measurements on PSII, and we have identified rate-limiting steps in the dark-to-light transition of PSII [1]. It was demonstrated in diuron-treated samples that the first STSF – generating the closed state (PSIIC) – induces only an F1(<Fm) fluorescence level, and additional excitations with sufficiently long Δτ waiting times between them are required to reach the maximum (Fm) level. We also revealed that the F1-to-Fm transition is linked to the gradual formation of the light-adapted charge-separated state, PSIIL, which possesses an increased stabilization of charges [2]. Recently, we studied the effects of different physicochemical environments of PSII on the half-rise time (Δτ1/2) and probed its presence during later steps (F2, F3 etc.) [3, 4]. In particular, we investigated the influence of the lipidic environment [3] and the temperature dependence of Δτ1/2 of PSII core complexes (CC) of Thermosynechococcus (T.) vulcanus and pea TMs [4]. We showed that (i) while non-native lipids has no effect, TM lipids shorten the Δτ1/2 of PSII CCs of T. vulcanus to that of TMs – uncovering the role of lipid matrix in the rate limiting steps; (ii) PSII CCs of T. vulcanus and spinach TMs exhibit very similar temperature dependences, with enhanced values at low temperatures; and (iii) the Δτ1/2 values in PSII CC are essentially independent at all temperatures on the number of the STSF-induced increments. These data suggest that the same physical mechanism is involved during the PSIIC-PSIILtransition.

References

[1] Magyar M et al. (2018) Sci Rep 8: 2755

[2] Sipka G et al. (2021) Plant Cell 33: 1286-1302.

[3] Magyar M et al. (2022) Photosynthetica 60: 147-156.

[4] Magyar M et al. (2022) IJMS 24: 94-104.

Steinbach Gábor
Anisotropy imaging using RCM

Aug 29 - kedd

15:30 – 17:00

I. Poszterszekció

P26

Anisotropy imaging using RCM

Gábor Steinbach1,2, Dávid Nagy3, Gábor Sipka2,4 , Ábel Garab2 , Győző Garab2,4 and László Zimányi3

1 ELKH, Biological Research Centre, Szeged, C ellular Imaging Laboratory

2 Biofotonika R&D Ltd.

3 ELKH, Biological Research Centre, Szeged, Institute of Biophysics

4 ELKH, Biological Research Centre, Szeged, Institute of Plant Biology

Both the differential polarization attachments for LSMs and Re-scan Confocal Microscopy (RCM) facilitate revealing structures at the molecular level [1]. For subcellular structures, increasing the available resolution can be fundamental. The re-scan confocal microscopy (RCM) provides 4 times better signal to noise ratio (compared to conventional PMTs) using an sCMOS camera, moreover, due to the second scanner, the image resolution increases by the factor of 1.4, while the axial resolution is identical with the LSMs [2].

With additional polarization elements, the RCM enables the 2D and 3D microscopic mapping of the anisotropy of samples via measuring fluorescence-detected linear dichroism (FDLD). The usage of the liquid crystal modulator for the RCM and the high frequency modulation (photoelastic modulator – PEM) are synchronised with the imaging. The DP-LSMs and the pRCM (RCM equipped with polarization attachment) are suitable for obtaining unique structural information on the anisotropic molecular organization of biological samples and intelligent materials [3, 4] in 2D and 3D.

References

[1] Steinbach et al. (2019) European Biophysics Journal 48: 457-463., doi: 10.1007/s00249-019-01365-4

[2] De Luca GMR et al. (2017) Methods Appl Fluoresc 5:015002., doi: 10.1088/2050-6120/5/1/015002

[3] Simonović Radosavljević J et al. (2021) Int. J. Mol. Sci. 22: 7661, doi: 10.3390/ijms22147661

[4] Pleckaitis M et al. (2022) Nano Research, 15: 5527-5537., doi: 10.1007/s12274-021-4048-x