Biology subjects

Natali, F.

Publications and source records attributed to Natali, F..

4 recordsLinked to original sources

bioRxiv2022

The dynamical Matryoshka model: 3. Diffusive nature of the atomic motions contained in a new dynamical model for deciphering local lipid dynamics

In accompanying papers [Bicout et al., BBA - Biomembr. Submitted; Cisse et al., BBA - Biomembr. Submitted], a new model called Matryoshka model has been proposed to describe the geometry of atomic motions in phospholipid molecules in bilayers and multilamellar vesicles based on their quasielastic neutron scattering (QENS) spectra. Here, in order to characterize the relaxational aspects of this model, the energy widths of the QENS spectra of the samples were analyzed first in a model-free way. The spectra were decomposed into three Lorentzian functions, which are classified as slow, intermediate, and fast motions depending on their widths. The analysis provides the diffusion coefficients, residence times, and geometrical parameters for the three classes of motions. The results corroborate the parameter values such as the amplitudes and the mobile fractions of atomic motions obtained by the application of the Matryoshka model to the same samples. Since the current analysis was carried out independently of the development of the Matryoshka model, the present results enhance the validity of the model. The model will serve as a powerful tool to decipher the dynamics of lipid molecules not only in model systems, but also in more complex systems such as mixtures of different kinds of lipids or natural cell membranes.

biophysics↗

bioRxiv2022

The dynamical Matryoshka model: 2. Modeling of local lipid dynamics at the sub-nanosecond timescale in phospholipid membranes

Biological membranes are generally formed by lipids and proteins. Often, the membrane properties are studied through model membranes formed by phospholipids only. They are molecules composed by a hydrophilic head group and hydrophobic tails, which can present a panoply of various motions, including small localized movements of a few atoms up to the diffusion of the whole lipid or collective motions of many of them. In the past, efforts were made to measure these motions experimentally by incoherent neutron scattering and to quantify them, but with upcoming modern neutron sources and instruments, such models can now be improved. In the present work, we expose a quantitative and exhaustive study of lipid dynamics on DMPC and DMPG membranes, using the Matryoshka model recently developed by our group. The model is confronted here to experimental data collected on two different membrane samples, at three temperatures and two instruments. Despite such complexity, the model describes reliably the data and permits to extract a series of parameters. The results compare also very well to other values found in the literature. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=81 SRC="FIGDIR/small/486370v1_fig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@374f9corg.highwire.dtl.DTLVardef@14ba37eorg.highwire.dtl.DTLVardef@dae67corg.highwire.dtl.DTLVardef@151f721_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 1:C_FLOATNO Graphical abstract. C_FIG Highlights- The Matryoshka model brings a new general description of local lipid dynamics. - Phospholipid membranes on various conditions are compared in this novel framework. - Effects of main phase transition, membrane geometry or motion direction are probed. - Despite high number of parameters, overfitting is avoided by a global fit strategy.

biophysics↗

bioRxiv2021

Strikingly different roles of SARS-CoV-2 fusion peptides uncovered by neutron scattering

Coronavirus disease-2019 (COVID-19), a lethal respiratory illness caused by the coronavirus SARS-CoV-2, emerged in the end of 2019 and has since spread aggressively across the globe. A thorough understanding of the molecular mechanisms of cellular infection by coronaviruses is therefore of utmost importance. A critical stage in infection is the fusion between viral and host membranes. Here, we present a detailed investigation of the role of the SARS-CoV-2 Spike protein, and the influence of calcium and cholesterol, in this fusion process. Structural information from specular neutron reflectometry and small angle neutron scattering, complemented by dynamics information from quasi-elastic and spin-echo neutron spectroscopy, revealed strikingly different functions encoded in the Spike fusion domain. Calcium drives the N-terminal of the Spike fusion domain to fully cross the host plasma membrane. Removing calcium however re-orients the protein to the lipid leaflet in contact with the virus, leading to significant changes in lipid fluidity and rigidity. In conjunction with other regions of the fusion domain which are also positioned to bridge and dehydrate viral and host membranes, the molecular events leading to cell entry by SARS-CoV-2 are proposed. SIGNIFICANCEWe have recreated here important elements of the critical membrane fusion mechanism of the SARS-CoV-2 coronavirus by simplifying the system down to its core elements, amenable to experimental analysis by neutron scattering. Neutrons are well suited for the study of protein - membrane interactions under physiological conditions, since they allow structural and dynamics characterization at room temperature. Our results revealed strikingly different functions encoded in the viral Spike fusion domain and thereby provide a potential calcium-dependent cell entry mechanism for SARS-CoV-2. In particular, calcium drives the proteins N-terminal to harpoon through the host membrane, while removing calcium re-orients the protein so that it is able to bridge and dehydrate lipid membranes, facilitating their fusion.

biophysics↗

bioRxiv2020

Epistasis, aneuploidy, and gain-of-function mutations underlie the evolution ofresistance to induced microtubule depolymerization

Microtubules, polymers of alpha- and beta-tubulin, are essential cellular components. When microtubule polymerization is hindered, cells are delayed in mitosis, but eventually they manage to proliferate with massive chromosome missegregation. Several studies have analyzed the first cell division upon microtubules impairing conditions. Here, we asked how cells cope on the long term. Taking advantage of mutations in beta-tubulin, we evolved in the lab for [~]150 generations 24 populations of yeast cells unable to properly polymerize microtubules. At the end of the evolution experiment, cells re-gained the ability to form microtubules, and were less sensitive to microtubule depolymerizing drugs. Whole genome sequencing allowed us to identify genes recurrently mutated (tubulins and kinesins) as well as the pervasive duplication of chromosome VIII. We confirmed that mutations found in these genes and disomy of chromosome VIII allow cells to compensate for the original mutation in beta-tubulin. The mutations we identified were mostly gain-of-function, likely re-allowing the proper use of the mutated form of beta-tubulin. When we analyzed the temporal order of mutations leading to resistance in independent populations, we observed multiple times the same series of events: disomy of chromosome VIII followed by one additional adaptive mutation in either tubulins or kinesins. Analyzing the epistatic interactions among different mutations, we observed that some mutations benefited from the disomy of chromosome VIII and others did not. Given that tubulins are highly conserved among eukaryotes, our results are potentially relevant for understanding the emergence of resistance to drugs targeting microtubules, widely used for cancer treatment.

cell biology↗