Exploring the World of Membrane Proteins: Techniques and Methods for Understanding Structure, Function, and Dynamics.

In eukaryotic cells, membrane proteins play a crucial role. They fall into three categories: intrinsic proteins, extrinsic proteins, and proteins that are essential to the human genome (30% of which is devoted to encoding them). Hydrophobic interactions inside the membrane serve to stabilize integral proteins, which span the lipid bilayer. This review investigates a number of computational and experimental methods used to study membrane proteins. It encompasses a variety of technologies, including electrophoresis, X-ray crystallography, cryogenic electron microscopy (cryo-EM), nuclear magnetic resonance spectroscopy (NMR), biophysical methods, computational methods, and artificial intelligence. The link between structure and function of membrane proteins has been better understood thanks to these approaches, which also hold great promise for future study in the field. The significance of fusing artificial intelligence with experimental data to improve our comprehension of membrane protein biology is also covered in this paper. This effort aims to shed light on the complexity of membrane protein biology by investigating a variety of experimental and computational methods. Overall, the goal of this review is to emphasize how crucial it is to understand the functions of membrane proteins in eukaryotic cells. It gives a general review of the numerous methods used to look into these crucial elements and highlights the demand for multidisciplinary approaches to advance our understanding.

Dielectric and Biological Characterization of Liver Tissue in a High-Fat Diet Mouse Model.

Hepatic steatosis may be caused by type 2 diabetes or obesity and is one of the origins of chronic liver disease. A non-invasive technique based on microwave propagation can be a good solution to monitor hepatic tissue pathologies. The present work is devoted to the dielectric permittivity measurements in healthy and fatty liver in the microwave range. A mouse model following normal and high sugar/glucose (HFS) diets was used. We demonstrated the change in the triglyceride and glucose concentration in the hepatic tissue of HFS diet mice. The difference in the dielectric permittivity of healthy and fatty liver was observed in the range from 100 MHz to 2 GHz. The dielectric permittivity was found to be 42 in the healthy tissue and 31 in the fatty liver tissue at 1 GHz. The obtained results demonstrate that dielectric permittivity can be a sensitive tool to distinguish between healthy and fatty hepatic tissue.

Evaporation Dynamics of Sessile Saline Microdroplets in Oil.

The occurrence of concentration and temperature gradients in saline microdroplets evaporating directly in air makes them unsuitable for nucleation studies where homogeneous composition is required. This can be addressed by immersing the droplet in oil under regulated humidity and reducing the volume to the picoliter range. However, the evaporation dynamics of such a system is not well understood. In this work, we present evaporation models applicable for arrays of sessile microdroplets with dissolved solute submerged in a thin layer of oil. Our model accounts for the variable diffusion distance due to the presence of the oil film separating the droplet and air, the variation of the solution density and water activity due to the evolving solute concentration, and the diffusive interaction between neighboring droplets. Our model shows excellent agreement with experimental data for both pure water and NaCl solution. With this model, we demonstrate that assuming a constant evaporation rate and neglecting the diffusive interactions can lead to severe inaccuracies in the measurement of droplet concentration, particularly during nucleation experiments. Given the significance of droplet evaporation in a wide array of scientific and industrial applications, the models and insights presented herein would be of great value to many fields of interest.

Impaired adhesion of neutrophils expressing Slc44a2/HNA-3b to VWF protects against NETosis under venous shear rates.

Genome-wide association studies linked expression of the human neutrophil antigen 3b (HNA-3b) epitope on the Slc44a2 protein with a 30% decreased risk of venous thrombosis (VT) in humans. Slc44a2 is a ubiquitous transmembrane protein identified as a receptor for von Willebrand factor (VWF). To explain the link between Slc44a2 and VT, we wanted to determine how Slc44a2 expressing either HNA-3a or HNA-3b on neutrophils could modulate their adhesion and activation on VWF under flow. Transfected HEK293T cells or neutrophils homozygous for the HNA-3a- or HNA-3b-coding allele were purified from healthy donors and perfused in flow chambers coated with VWF at venous shear rates (100 s-1). HNA-3a expression was required for Slc44a2-mediated neutrophil adhesion to VWF at 100 s-1. This adhesion could occur independently of ß2 integrin and was enhanced when neutrophils were preactivated with lipopolysaccharide. Moreover, specific shear conditions with high neutrophil concentration could act as a "second hit," inducing the formation of neutrophil extracellular traps. Neutrophil mobilization was also measured by intravital microscopy in venules from SLC44A2-knockout and wild-type mice after histamine-induced endothelial degranulation. Mice lacking Slc44a2 showed a massive reduction in neutrophil recruitment in inflamed mesenteric venules. Our results show that Slc44a2/HNA-3a is important for the adhesion and activation of neutrophils in veins under inflammation and when submitted to specific shears. The fact that neutrophils expressing Slc44a2/HNA-3b have a different response on VWF in the conditions tested could thus explain the association between HNA-3b and a reduced risk for VT in humans.

Microfluidic device to study flow-free chemotaxis of swimming cells.

Microfluidic devices have been used in the last two decades to study in vitro cell chemotaxis, but few existing devices generate gradients in flow-free conditions. Flow can bias cell directionality of adherent cells and precludes the study of swimming cells like naïve T lymphocytes, which only migrate in a non-adherent fashion. We developed two devices that create stable, flow-free, diffusion-based gradients and are adapted for adherent and swimming cells. The flow-free environment is achieved by using agarose gel barriers between a central channel with cells and side channels with chemoattractants. These barriers insulate cells from injection/rinsing cycles of chemoattractants, they dampen residual drift across the device, and they allow co-culture of cells without physical interaction, to study contactless paracrine communication. Our devices were used here to investigate neutrophil and naïve T lymphocyte chemotaxis.

Water interaction with hydrophobic and hydrophilic soot particles.

The interaction of water with laboratory soots possessing a range of properties relevant for atmospheric studies is examined by two complementary methods: gravimetrical measurement of water uptake coupled with chemical composition and porosity analysis and HTDMA (humidified tandem differential mobility analyzer) inference of water uptake accompanied by separate TEM (transmission electron microscopy) analysis of single particles. The first method clarifies the mechanism of water uptake for bulk soot and allows the classification of soot with respect to its hygroscopicity. The second method highlights the dependence of the soot aerosol growth factor on relative humidity (RH) for quasi-monodisperse particles. Hydrophobic and hydrophilic soot are qualitatively defined by their water uptake and surface polarity: laboratory soot particles are thus classified from very hydrophobic to very hydrophilic. Thermal soot particles produced from natural gas combustion are classified as hydrophobic with a surface of low polarity since water is found to cover only half of the surface. Graphitized thermal soot particles are proposed for comparison as extremely hydrophobic and of very low surface polarity. Soot particles produced from laboratory flame of TC1 aviation kerosene are less hydrophobic, with their entire surface being available for statistical monolayer water coverage at RH approximately 10%. Porosity measurements suggest that, initially, much of this surface water resides within micropores. Consequently, the growth factor increase of these particles to 1.07 at RH > 80% is attributed to irreversible swelling that accompanies water uptake. Hysteresis of adsorption/desorption cycles strongly supports this conclusion. In contrast, aircraft engine soot, produced from burning TC1 kerosene in a gas turbine engine combustor, has an extremely hydrophilic surface of high polarity. Due to the presence of water soluble organic and inorganic material it can be covered by many water layers even below water saturation conditions. This soot demonstrates a gradual diameter growth factor (D(wet)/D(dry)) increase up to 1.22 at 93% relative humidity, most likely due to the presence of single particles with water soluble material heterogeneously distributed over their surface.