Biology subjects

Heux, L.

Publications and source records attributed to Heux, L..

3 recordsLinked to original sources

bioRxiv2024

Optical sectioning for reflection interference microscopy

Reflection Interference Contrast Microscopy (RICM, also known as interference reflection microscopy) and related techniques have become of wide interest to the biophysical, soft matter and biochemistry communities owing to their exquisite sensitivity for characterising thin films or individual nanoscopic objects adsorbed onto surfaces, or for monitoring cell-substrate interactions. Over the recent years, striking progresses have been made to improve the sensitivity and the quantitative analysis of RICM. Its use in more complex environments, with spurious reflections stemming from a variety of structures in the sample, remains however challenging. In this paper, we demonstrate two optical sectioning methods that effectively reduce such background and can be readily implemented in a conventional RICM setup: line confocal detection, and structured illumination microscopy. We characterise experimentally the benefits to image quality and demonstrate the use of the methods for quantitative imaging of complex biological and biomimetic samples: cellular membranes, thin organic films, surface biofunctionalization. We then discuss the benefits of each method and provide guidelines to arbitrate between sectioning and signal-to-noise ratio. Finally, we provide a detailed description of our experimental setup and a home-written image acquisition and processing software that should allow the interested reader to duplicate such a setup on a home-built or commercial microscope.

biophysics↗

bioRxiv2022

Building artificial plant cell wall on lipid bilayer by assembling polysaccharides and engineered proteins

The cell wall constitutes a fundamental structural component of plant cells, providing them with mechanical resistance and flexibility. Mimicking that wall is a critical step in the conception of an experimental model of the plant cell. The assembly of cellulose/hemicellulose in the form of cellulose nanocrystals and xyloglucans as a representative model of the plant cell wall has already been mastered, however, those models lacked the pectin component. In this work, we used an engineered chimeric protein designed for bridging pectin to the cellulose/hemicellulose network, therefore achieving the assembly of complete cell wall mimics. We first engineered proteins, i.e. carbohydrate-binding module from Ruminococcus flavefaciens able to bind oligo-galactorunan, resulting in high-affinity polygalacturonan receptors with Kd in the micromolar range. A Janus protein, with cell wall gluing property, was then designed by assembling this CBM with a Ralstonia solanacearum lectin specific for fucosylated xyloglucans. The resulting supramolecular architecture is able to bind fucose-containing xyloglucans and homogalacturonan ensuring high affinity for both. A two-dimension assembly of an artificial plant cell wall was then built first on synthetic polymer and then on supported lipid bilayer. Such artificial cell wall can serve as a basis for the development of plant cell mechanical models and thus deepen the understanding of the principles underlying various aspects of plant cells and tissues. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=123 HEIGHT=200 SRC="FIGDIR/small/501355v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@18af594org.highwire.dtl.DTLVardef@ec3dorg.highwire.dtl.DTLVardef@95d44aorg.highwire.dtl.DTLVardef@a47bea_HPS_FORMAT_FIGEXP M_FIG C_FIG

synthetic biology↗

bioRxiv2020

Purification, characterization and influence on membrane properties of the plant-specific sphingolipids GIPC

The plant plasma membrane (PM) is an essential barrier between the cell and the external environment. The PM is crucial for signal perception and transmission. It consists of an asymmetrical lipid bilayer made up of three different lipid classes: sphingolipids, sterols and phospholipids. The most abundant sphingolipids in the plant PM are the Glycosyl Inositol Phosphoryl Ceramides (GIPCs), representing up to 40% of total sphingolipids, assumed to be almost exclusively in the outer leaflet of the PM. In this study, we investigated the structure of GIPCs and their role in membrane organization. Since GIPCs are not commercially available, we developed a protocol to extract and isolate GIPC-enriched fractions from eudicots (cauliflower and tobacco) and monocots (leek and rice). Lipidomic analysis confirmed the presence of different long chain bases and fatty acids. The glycan head groups of the different GIPC series from monocots and dicots were analysed by GC-MS showing different sugar moieties. Multiple biophysics tools namely Langmuir monolayer, {zeta}-Potential, light scattering, neutron reflectivity, solid state 2H-NMR and molecular modelling were used to investigate the physical properties of the GIPCs, as well as their interaction with free and conjugated phytosterols. We showed that GIPCs increase the thickness and electronegativity of model membranes, interact differentially with the phytosterols species and regulate the gel-to-fluid phase transition during temperature variations.

plant biology↗