Biology subjects

Franquelim, H. G.

Publications and source records attributed to Franquelim, H. G..

5 recordsLinked to original sources

bioRxiv2023

DNA Origami Vesicle Sensors with Triggered Cargo Transfer

Interacting with living systems typically involves the ability to address lipid membranes of cellular systems. The first step of interaction of a nanorobot with a cell will thus be the detection of binding to a lipid membrane. Leveraging the programmable nature of DNA origami, we engineered a biosensor harnessing single-molecule Fluorescence Resonance Energy Transfer (smFRET) as transduction mechanism for precise lipid vesicle detection. The system hinges on a hydrophobic ATTO647N modified single-stranded DNA (ssDNA) leash, protruding from a rectangular DNA origami. In a vesicle-free environment, the ssDNA adopts a coiled stance, ensuring high FRET efficiency. However, upon lipid vesicle binding to cholesterol anchors on the DNA origami, the hydrophobic ATTO647N induces the ssDNA to stretch towards the lipid bilayer, leading to reduced FRET efficiency. The strategic placement of cholesterol anchors further modulates this interaction, affecting the observed FRET populations. Beyond its role as a vesicle sensor, we show targeted cargo transport of the acceptor dye unit to the vesicle. The cargo transport is initiated by vesicle bound DNA and a strand displacement reaction. Our interaction platform opens pathways for innovative interaction such as biosensing and molecular transport with complex biosystems.

bioengineering↗

bioRxiv2023

Nanoscale structural response of biomimetic cell membranes to controlled dehydration.

Although cell membranes in physiological conditions exist in excess of water, there is a number of biochemical processes, such as adsorption of biomacromolecules or membrane fusion events, that require partial or even complete, transient dehydration of lipid membranes. Even though the dehydration process is crucial for understanding all fusion events, still little is known about the structural adaptation of the lipid membranes when their interfacial hydration layer is perturbed. Here, we introduce the study on the nanoscale structural reorganization of the phase-separated, supported lipid bilayers (SLBs) under a wide range of hydration conditions. Model lipid membranes were characterized with the combination of fluorescence microscopy and atomic force microscopy, and crucially, without applying any chemical or physical modifications, that so far have been considered to be indispensable for maintaining the membrane integrity upon dehydration. We revealed that decreasing hydration state of the membrane leads to an enhanced mixing of lipids characteristic for the liquid-disordered (Ld) phase with those forming liquid-ordered (Lo) phase. This is associated with a 2-fold decrease in the hydrophobic mismatch between the Ld and Lo lipid phases and a 3-fold decrease of line tension for the completely desiccated membrane. Importantly, the observed changes in the hydrophobic mismatch, line tension, and miscibility of lipids are fully reversible upon subsequent rehydration of the membrane. These findings provide deeper insights into the fundamental processes such as cell-cell fusion that require partial dehydration at the interface of two membranes.

biophysics↗

bioRxiv2021

Structural Diversity of Photoswitchable Sphingolipids for Optodynamic Control of Lipid Raft Microdomains

Sphingolipids are a structurally diverse class of lipids predominantly found in the plasma membrane of eukaryotic cells. These lipids can laterally segregate with other saturated lipids and cholesterol into lipid rafts; liquid-ordered (Lo) microdomains that act as organizing centers within biomembranes. Owing the vital role of sphingolipids for lipid segregation, controlling their lateral localization is of utmost significance. Hence, we made use of the light-induced trans-cis isomerization of azobenzene-modified acyl chains, to develop a set of photoswitchable sphingolipids, with different headgroups (hydroxyl, galactosyl, phosphocholine) and backbones (sphingosine, phytosphingosine, tetrahydropyran (THP)-blocked sphingosine), able to shuttle between liquid-ordered (Lo) and liquid-disordered (Ld) regions of model membranes upon irradiation with UV-A ({lambda} = 365 nm) and blue ({lambda} = 470 nm) light, respectively. Using combined high-speed atomic force microscopy, fluorescence microscopy, and force spectroscopy, we investigated how these active sphingolipids laterally remodel supported bilayers upon photo-isomerization, notably in terms of domain area changes, height mismatch, line tension, and membrane piercing. Hereby, we show that all sphingosine-(Azo-{beta}-Gal-Cer, Azo-SM, Azo-Cer) and phytosphingosine-based (Azo--Gal-PhCer, Azo-PhCer) photolipids behave similarly, promoting a reduction in Lo domain area when in the UV-adapted cis-isoform. In contrast, azo-sphingolipids having THP groups that block H-bonding at the sphingosine backbone (Azo-THP-SM, Azo-THP-Cer) induce an increase in the Lo domain area when in cis, accompanied by a major rise in height mismatch and line tension. These changes were fully reversible upon blue light-triggered isomerization of the various lipids back to trans, pinpointing the role of interfacial interactions for the formation of stable Lo lipid raft domains.

biophysics↗

bioRxiv2021

DNA Origami Voltage Sensors for Transmembrane Potentials with Single-Molecule Sensitivity

Signal transmission in neurons goes along with changes in the transmembrane potential. To report them, different approaches including optical voltage-sensing dyes and genetically encoded voltage indicators have evolved. Here, we present a DNA nanotechnology-based system. Using DNA origami, we incorporate and optimize different properties such as membrane targeting and voltage sensing modularly. As a sensing unit, we use a hydrophobic red dye anchored to the membrane and an anionic green dye at the DNA connecting the DNA origami and the membrane dye anchor. Voltage-induced displacement of the anionic donor unit is read out by changes of Fluorescence Resonance Energy Transfer (FRET) of single sensors attached to liposomes. They show a FRET change of [~]5% for {Delta}{Psi}=100 mV and allow adapting the potential range of highest sensitivity. Further, the working mechanism is rationalized by molecular dynamics simulations. Our approach holds potential for the application as non-genetically encoded sensors at membranes.

biophysics↗

bioRxiv2021

Hydration layer of only few molecules controls lipid mobility in biomimetic membranes

Self-assembly of biomembranes results from the intricate interactions between water and the lipids hydrophilic head groups. Therefore, the lipid-water interplay strongly contributes to modulating membranes architecture, lipid diffusion, and chemical activity. Here, we introduce a new method of obtaining dehydrated, phase-separated, supported lipid bilayers (SLBs) solely by controlling the decrease of their environments relative humidity. This facilitates the study of the structure and dynamics of SLBs over a wide range of hydration states. We show that the lipid domain structure of phase-separated SLBs is largely insensitive to the presence of the hydration layer. In stark contrast, lipid mobility is drastically affected by dehydration, showing a 6-fold decrease in lateral diffusion. At the same time, the diffusion activation energy increases approximately twofold for the dehydrated membrane. The obtained results, correlated with the hydration structure of a lipid molecule, revealed that about 6-7 water molecules directly hydrating the phosphocholine moiety play a pivotal role in modulating lipid diffusion. These findings could provide deeper insights into the fundamental reactions where local dehydration occurs, for instance during cell-cell fusion, and help us better understand the survivability of anhydrobiotic organisms. Finally, the strong dependence of lipid mobility on the number of hydrating water molecules opens up an application potential for SLBs as very precise, nanoscale hydration sensors.

biophysics↗