Following the structural changes during zinc-induced crystallization of charged membranes using time-resolved solution X-ray scattering

Nadler, Moshe; Steiner, Ariel; Dvir, Tom; Szekely, Or; Szekely, Pablo; Ginsburg, Avi; Asor, Roi; Resh, Roy; Tamburu, Carmen; Peres, Menahem; Raviv, Uri

doi:10.1039/c0sm00824a

Cited by 57 publications

(97 citation statements)

References 39 publications

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“…High-resolution SAXS was performed as described in ref. 59. SANS was performed at the KWS-2 instrument operated by Jülich Centre for Neutron Science (JCNS) at the Heinz Maier-Leibnitz Zentrum, Garching, Germany (60, 61) (SI Text).…”

Section: Methodsmentioning

confidence: 99%

Changes in aggregation states of light-harvesting complexes as a mechanism for modulating energy transfer in desert crust cyanobacteria

Eyal

Choubeh

Cohen

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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In this paper we propose an energy dissipation mechanism that is completely reliant on changes in the aggregation state of the phycobilisome light-harvesting antenna components. All photosynthetic organisms regulate the efficiency of excitation energy transfer (EET) to fit light energy supply to biochemical demands. Not many do this to the extent required of desert crust cyanobacteria. Following predawn dew deposition, they harvest light energy with maximum efficiency until desiccating in the early morning hours. In the desiccated state, absorbed energy is completely quenched. Time and spectrally resolved fluorescence emission measurements of the desiccated desert crust Leptolyngbya ohadii strain identified (i) reduced EET between phycobilisome components, (ii) shorter fluorescence lifetimes, and (iii) red shift in the emission spectra, compared with the hydrated state. These changes coincide with a loss of the ordered phycobilisome structure, evident from small-angle neutron and X-ray scattering and cryo-transmission electron microscopy data. Based on these observations we propose a model where in the hydrated state the organized rod structure of the phycobilisome supports directional EET to reaction centers with minimal losses due to thermal dissipation. In the desiccated state this structure is lost, giving way to more random aggregates. The resulting EET path will exhibit increased coupling to the environment and enhanced quenching.eserts cover almost half of the Earth's terrestrial surface, and although desert conditions may seem unfavorable, they are home for diverse ecosystems. Many of these ecosystems are founded on biological desert crusts, which play an essential role in stabilizing shifting sands and enriching them with nutrients (1, 2). Cyanobacteria are among the first microorganisms to inhabit these crusts where one of the major sources of water is often dew deposited before dawn (3, 4). However, as temperatures elevate, water quickly evaporates. Such conditions can be extremely harmful for photosynthetic organisms and require adaptations on all cellular levels (3-9). These include shifts in metabolic profiles and the accumulation of compatible solutes. A key issue is the adaptation of the photosynthetic apparatus because continued photosynthetic activity under high light, and especially in combination with desiccation, may lead to the production of reactive oxygen species that will cause damage to the entire cell (10-12). The cyanobacteria that colonize sand crusts evolved strategies for coping with these daily cycles of hydration using mechanisms that enable extensive quenching of absorbed light energy. The extent of quenching in these organisms far exceeds that of common laboratory model organisms (13, 14).Our studies focused on Leptolyngbya ohadii, a crust cyanobacterium isolated from the Nizzana region of the NW Negev desert in Israel (3,6). This is a keystone organism in this environment (4). To maintain L. ohadii cells in a viable state the desiccation process must be gradual (3). Recovery o...

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Section: Methodsmentioning

confidence: 99%

Changes in aggregation states of light-harvesting complexes as a mechanism for modulating energy transfer in desert crust cyanobacteria

Eyal

Choubeh

Cohen

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…The SAXS-derived estimates for the bilayer membrane thicknesses are listed in Table 1. For C 16 mixtures, the bilayer thickness is highest at pH 3 (∼5.8 nm). For pH ≥ 6.5, the bilayer thickness is nearly a constant ∼4.0 nm.…”

Section: Resultsmentioning

confidence: 99%

“…S2). Similar to the case of C 16 , mixtures of C 14 , C 18 , C 20 , and C 22 , each coassemble into bilayers that are stable over long periods (days). The SAXS data are fitted using a model that accounts for both bilayer membranes and spherical micelles (see SI Appendix for details).…”

Section: Resultsmentioning

confidence: 99%

“…As the tail length increases, the hexagonal lattice spacing decreases due to an increase in van der Waals interactions, as demonstrated by atomistic molecular dynamics simulations. For C 16 and C 18 we observe a reentrant crystalline phase transition sequence, hexagonalrectangular-C-rectangular-P-rectangular-C-hexagonal, as the solution pH is increased from 3 to 10.5. The stability of the rectangular phases, which maximize tail packing, increases with increasing tail length.…”

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confidence: 94%

“…The presence of polar and hydrophobic groups in their wall envelopes and the fact that they survive at low pH values and disintegrate or become spherical (the shape of closed liquid membranes) when divalent metal ions are chelated (11,13) suggest that their crystallization is triggered by electrostatic interactions. Divalent ion-induced crystallization of anionic membranes has been recently studied (16,17), but crystallization changes induced by pH variations in bilayers are unknown. Here, we study pH effects in crystalline membranes of coassembled amphiphiles with carboxylate and dilysine headgroups, whose pK a values are about 5.5 (18) and 10 (19), respectively.…”

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Crystalline polymorphism induced by charge regulation in ionic membranes

Leung

Palmer

Kewalramani

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The crystallization of molecules with polar and hydrophobic groups, such as ionic amphiphiles and proteins, is of paramount importance in biology and biotechnology. By coassembling dilysine (+2) and carboxylate (-1) amphiphiles of various tail lengths into bilayer membranes at different pH values, we show that the 2D crystallization process in amphiphile membranes can be controlled by modifying the competition of long-range and shortrange interactions among the polar and the hydrophobic groups. The pH and the hydrophobic tail length modify the intermolecular packing and the symmetry of their crystalline phase. For hydrophobic tail lengths of 14 carbons (C 14 ), we observe the coassembly into crystalline bilayers with hexagonal molecular ordering via in situ small-and wide-angle X-ray scattering. As the tail length increases, the hexagonal lattice spacing decreases due to an increase in van der Waals interactions, as demonstrated by atomistic molecular dynamics simulations. For C 16 and C 18 we observe a reentrant crystalline phase transition sequence, hexagonalrectangular-C-rectangular-P-rectangular-C-hexagonal, as the solution pH is increased from 3 to 10.5. The stability of the rectangular phases, which maximize tail packing, increases with increasing tail length. As a result, for very long tails (C 22 ), the possibility of observing packing symmetries other than rectangular-C phases diminishes. Our work demonstrates that it is possible to systematically exchange chemical and mechanical energy by changing the solution pH value within a range of physiological conditions at room temperature in bilayers of molecules with ionizable groups.amphiphilic membranes | self-assembly | hydrophobic interaction N ature uses electrostatic interactions among positively and negatively charged groups to induce the organization of biomolecules into highly complex structures that respond to ionic changes (1, 2). The structure of the aggregates at specific ionic conditions is intimately related to its function. Therefore, understanding the mechanisms that control the structure of molecules with hydrophobic and polar groups at physiological conditions is of great importance in molecular biology and biotechnology. In particular, amphiphilic molecules that have polar ionizable groups, such as proteins and lipids, can change their structures and functions in response to the pH and the concentration of ions in the solution (3), thereby affecting their physical properties and functions. For example, the structure of lipid membranes affects the structure and activity of membrane-bound proteins (4-6). Furthermore, the intermolecular packing density and structure are known to affect the molecular diffusion rates of water and ions across membranes (7,8). Changing the packing density of molecules within membranes could also be useful for controlling encapsulation and release efficiency of molecules inside a vesicle (9). Additionally the spacing between amphiphilic molecules within a membrane may control the capacity to encapsulate or release...

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Solution X‐ray Scattering Form‐Factors with Arbitrary Electron Density Profiles and Polydispersity Distributions

Ben-Nun

Asor

Ginsburg

et al. 2015

Israel Journal of Chemistry

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multiple spherical shells and compare the results to show the consistency of the algorithm. Other geometries are solved numerically. Various form-factors are analysed and compared with earlier results. We then compare polydispersity probability density functions (uniform, normal, and Cauchy distributions) of concentric hollow cylinder thicknesses. The relationship of the shape of arbitrary electron density profiles to the features of the scattering form-factor is discussed.Keywords: density functional calculations · generalized electron density · SAXS · self-assembly · solution X-ray scattering[a] T.

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Following the structural changes during zinc-induced crystallization of charged membranes using time-resolved solution X-ray scattering

Cited by 57 publications

References 39 publications

Changes in aggregation states of light-harvesting complexes as a mechanism for modulating energy transfer in desert crust cyanobacteria

Changes in aggregation states of light-harvesting complexes as a mechanism for modulating energy transfer in desert crust cyanobacteria

Crystalline polymorphism induced by charge regulation in ionic membranes

Solution X‐ray Scattering Form‐Factors with Arbitrary Electron Density Profiles and Polydispersity Distributions

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