Biomolecular condensates modulate membrane lipid packing and hydration

Abstract

Membrane wetting by biomolecular condensates recently emerged as a key phenomenon in cell biology, playing an important role in a diverse range of processes across different organisms. However, an understanding of the molecular mechanisms behind condensate formation and interaction with lipid membranes is still missing. To study this, we exploited the properties of the dyes ACDAN and LAURDAN as nano-environmental sensors in combination with phasor analysis of hyperspectral and lifetime imaging microscopy. Using glycinin as a model condensate-forming protein and giant vesicles as model membranes, we obtained vital information on the process of condensate formation and membrane wetting. Our results reveal that glycinin condensates display differences in water dynamics when changing the salinity of the medium as a consequence of rearrangements in the secondary structure of the protein. Remarkably, analysis of membrane-condensates interaction with protein as well as polymer condensates indicated a correlation between increased wetting affinity and enhanced lipid packing. This is demonstrated by a decrease in the dipolar relaxation of water across all membrane-condensate systems, suggesting a general mechanism to tune membrane packing by condensate wetting.

Transmembrane coupling of liquid-like protein condensates

“…Why are diverse probe lipids excluded from the protein-enriched phase? Probe exclusion arises due to the local reorganization of lipids, which could encompass changes in lipid packing 31 , 32 , lipid composition (enrichment of DGS-Ni-NTA lipids in protein-rich regions), or the degree of lipid hydration owing to the presence of proteins 33 , each via protein-lipid interactions. To quantify the extent of probe lipid exclusion, we defined a partition coefficient (K P ) as K P = I B / I D , where I B and I D indicate the fluorescence intensity of the brighter and the dimmer regions in the lipid channel after subtracting the background intensity, respectively 34 .…”

The biophysics of water in cell biology: perspectives on a keystone for both marine sciences and cancer research

“…Salinity or membrane composition also tune the interactions between biomolecular condensates and membranes, a reciprocal mechanism existing between water activity and supramolecular rearrangement, with protein secondary structure altering water dynamics in turn ( Mangiarotti et al, 2023 ). The way biomolecular condensation of intrinsically disordered proteins controls water availability in cells was also investigated ( De Souza and Stone, 2023 ; Watson et al, 2023 ).…”

Extracellular vesicle mobility in collagen I hydrogels is influenced by RGD-binding integrins

“…LAURDAN is a lipophilic fluorescent probe whose emission spectrum is sensitive to the molecular environment of the lipid bilayer into which it is inserted. 43,52,53 Differences in membrane phase state, hydration, or lipid packing can be represented in graphical form using phasor analysis, which decomposes the spectral shifts into the Cartesian coordinates, G and S. [54][55][56][57][58] For comparison and to better understand the differences between EVs and synthetic systems, we have also analyzed synthetic multilamellar lipid-only vesicles composed of pure 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC); a binary mixture of 70% DOPC and 30% cholesterol (DOPC+Chol); and a ternary mixture of 13% DOPC, 44% Dipalmitoylphosphatidylcholine (DPPC), and 43% cholesterol (Ternary L o ). While DOPC and DOPC+Chol represent lipid membranes in the liquid-disordered (L d ) phase state, the Ternary L o mixture represents a liquid-ordered lipid membrane, referring to the molecular packing in the lipid bilayer and order in the hydrophobic fatty acid tails.…”

“…EVs and LPMVs labelled with 0.5mol% LAURDAN were loaded in a quartz crystal cuvette (Hellma, Germany) and their fluorescence spectra were measured with 360nm excitation using a FluoroMax Plus Spectrofluorometer (Horiba, Japan). The spectral information were then converted to phasor coordinates, as previously reported [55][56][57] with the following equations:…”