Computational investigation for endocytosis of CoVID-19 virus SARS-CoV-2 in cell membrane

CoVID-19 virus SARS-CoV-2 follows the endocytosis process to enter inside a cell to infect it. It is important to study the endocytosis of SARS-CoV-2 in cell membrane to prevent the pandemic of CoVID-19. In this paper we develop a finite element based computational model for endocytosis of SARS-CoV-2 in cell membrane and determine curvature generation on it during the process. The virus SARS-CoV-2 is modeled as a rigid spherical particle and cell membrane as an anisotropic elastic material, while its fluidic nature due to lipid exchange with infinite reservoir is preserved using suitable conditions. With the help of a contact pair created between the virus particle and cell membrane, endocytosis process is computationally studied and the curvature of membrane is evaluated as the time progresses during the endocytosis process. At the tip of the virus particle and half-radius distance from it, the membrane follows the curvature of virus very quickly. However, it takes more time for the membrane point located at a distance equal to the radius of the virus particle. This is compensated by the cytoplasmic peripheral proteins binding onto the inside surface of the cell membrane. The role of cytoplasmic peripheral BAR proteins is investigated by using a linear curvature-coupling model with protein concentrations. It is observed that F-BAR protein is more sensitive to the curvature of virus particle in comparison to the other BAR proteins. The sensitiveness deteriorates as the curvature is increased.

Quantitative analysis of membrane-mediated interactions and aggregation of flexible peripheral proteins orchestrating large-scale membrane remodeling

Shaping and remodeling of biomembranes is essential for cellular trafficking, with membrane-binding peripheral proteins playing the key role in it. Significant membrane remodeling as in endo- and exocytosis is often due to clusters or aggregates of many proteins whose interactions may be direct or mediated via the membrane. While computer simulation could be an important tool to disentangle these interactions and understand what drives cooperative protein interactions in membrane remodeling, this has so far been extremely challenging: protein-membrane systems involve time- and lengthscales that make detailed atomistic simulations impractical, while most coarse-grained models lack the degree of detail needed to resolve the dynamics and physical effect of protein and membrane flexibility. Here, we develop a coarse-grained model of the bilayer membrane bestrewed with rotationally-symmetric flexible membrane-bound proteins. We show how this model can be parameterized based on local curvatures, protein flexibility, and the in-plane dynamics of proteins. We measure the effective interaction potential for the membrane-mediated interactions between peripheral proteins. Furthermore, we investigate the kinetics, equilibrium distributions, and the free energy landscape governing the formation and break-up of protein clusters on the surface of the membrane. We demonstrate how the flexibility of the protein plays a deciding role in highly selective macroscopic aggregation behavior. Finally, we present large-scale simulations of membrane tubulation, and discuss the sequence of events and the stability of intermediates.

Quantitative analysis of membrane-mediated interactions and aggregation of flexible peripheral proteins orchestrating large-scale membrane remodeling

Shaping and remodeling of biomembranes is essential for cellular trafficking, with membrane-binding peripheral proteins playing the key role in it. Significant membrane remodeling as in endo- and exocytosis is often due to clusters or aggregates of many proteins whose interactions may be direct or mediated via the membrane. While computer simulation could be an important tool to disentangle these interactions and understand what drives cooperative protein interactions in membrane remodeling, this has so far been extremely challenging: protein-membrane systems involve time- and lengthscales that make detailed atomistic simulations impractical, while most coarse-grained models lack the degree of detail needed to resolve the dynamics and physical effect of protein and membrane flexibility. Here, we develop a coarse-grained model of the bilayer membrane bestrewed with rotationally-symmetric flexible membrane-bound proteins. We show how this model can be parameterized based on local curvatures, protein flexibility, and the in-plane dynamics of proteins. We measure the effective interaction potential for the membrane-mediated interactions between peripheral proteins. Furthermore, we investigate the kinetics, equilibrium distributions, and the free energy landscape governing the formation and break-up of protein clusters on the surface of the membrane. We demonstrate how the flexibility of the protein plays a deciding role in highly selective macroscopic aggregation behavior. Finally, we present large-scale simulations of membrane tubulation, and discuss the sequence of events and the stability of intermediates.

Interaction of Peptides Containing CRAC Motifs with Lipids in Membranes of Various Composition

The lateral distribution of integral and peripheral proteins, as well as lipids in the plasma membranes of mammalian cells is extremely heterogeneous. It is believed that various lipid-protein domains are formed in membranes. Domains enriched in sphingomyelin and cholesterol are called rafts. It is assumed that the distribution of proteins into rafts is largely related to the presence in their primary sequence of a specific amino acid region called the CRAC motif, which is responsible for cholesterol binding. In this work, the interaction of two peptides containing CRAC motifs in their structure with membranes of different compositions was studied by means of molecular dynamics. It has been shown that the average number of lipid molecules in contact with each peptide is proportional to the mole fraction of lipid in the membrane. The predominant interaction of peptides with cholesterol was not observed. In addition, cholesterol did not form long-lived contacts with any amino acid or amino acid sequence. We suppose that in some cases the predominant lateral distribution of peptides and proteins containing CRAC motifs into rafts may be due to amphipathicity of the CRAC motif rather than due to specific strong binding of cholesterol.

Divalent cations bind to phosphoinositides to induce ion and isomer specific propensities for nano-cluster initiation in bilayer membranes

We report all-atom molecular dynamics simulations of asymmetric bilayers containing phosphoinositides in the presence of monovalent and divalent cations. We have characterized the molecular mechanism by which these divalent cations interact with phosphoinositides. Ca 2+ desolvates more readily, consistent with single-molecule calculations, and forms a network of ionic-like bonds that serve as a ‘molecular glue’ that allows a single ion to coordinate with up to three phosphatidylinositol-(4,5)-bisphosphate (PI(4, 5)P 2 ) lipids. The phosphatidylinositol-(3,5)-bisphosphate isomer shows no such effect and neither does PI(4, 5)P 2 in the presence of Mg 2+ . The resulting network of Ca 2+ -mediated lipid-lipid bonds grows to span the entire simulation space and therefore has implications for the lateral distribution of phosophoinositides in the bilayer. We observe context-specific differences in lipid diffusion rates, lipid surface densities and bilayer structure. The molecular-scale delineation of ion-lipid arrangements reported here provides insight into similar nanocluster formation induced by peripheral proteins to regulate the formation of functional signalling complexes on the membrane.

Membrane Lipid Switches: How Membrane Lipid Structure Influences Protein–Lipid Interactions

Peripheral membrane proteins are required for signal propagation upon ligand-induced receptor activation at the plasma membrane. The translocation of this amphitropic peripheral proteins from or to the plasma membrane enables signal cascade propagation into the cells. This translocation greatly depends on the membrane’s lipid composition and, consequently, regulation of the lipid bilayer emerges as a novel therapeutic strategy. Indeed, relevant changes in membrane lipids can induce massive translocation of peripheral signaling proteins from or to the plasma membrane, which controls how cells behave. We called these changes “lipid switches”, as they alter the cell’s status (e.g., proliferation, differentiation, death, etc.) in response to the modulation of membrane lipids. This discovery enables therapeutic interventions focused on modifying the bilayer’s lipids, an approach known as membrane-lipid therapy (MLT) or melitherapy.

The Implications for Cells of the Lipid Switches Driven by Protein–Membrane Interactions and the Development of Membrane Lipid Therapy

The cell membrane contains a variety of receptors that interact with signaling molecules. However, agonist–receptor interactions not always activate a signaling cascade. Amphitropic membrane proteins are required for signal propagation upon ligand-induced receptor activation. These proteins localize to the plasma membrane or internal compartments; however, they are only activated by ligand-receptor complexes when both come into physical contact in membranes. These interactions enable signal propagation. Thus, signals may not propagate into the cell if peripheral proteins do not co-localize with receptors even in the presence of messengers. As the translocation of an amphitropic protein greatly depends on the membrane’s lipid composition, regulation of the lipid bilayer emerges as a novel therapeutic strategy. Some of the signals controlled by proteins non-permanently bound to membranes produce dramatic changes in the cell’s physiology. Indeed, changes in membrane lipids induce translocation of dozens of peripheral signaling proteins from or to the plasma membrane, which controls how cells behave. We called these changes “lipid switches”, as they alter the cell’s status (e.g., proliferation, differentiation, death, etc.) in response to the modulation of membrane lipids. Indeed, this discovery enables therapeutic interventions that modify the bilayer’s lipids, an approach known as membrane-lipid therapy (MLT) or melitherapy.

Intracellular Background Estimation for Quantitative Fluorescence Microscopy

Fluorescently targeted proteins are widely used for studies of intracellular organelles dynamic. Peripheral proteins are transiently associated with organelles and a significant fraction of them are located at the cytosol. Image analysis of peripheral proteins poses a problem on properly discriminating membrane-associated signal from the cytosolic one. In most cases, signals from organelles are compact in comparison with diffuse signal from cytosol. Commonly used methods for background estimation depend on the assumption that background and foreground signals are separable by spatial frequency filters. However, large non-stained organelles (e.g., nuclei) result in abrupt changes in the cytosol intensity and lead to errors in the background estimation. Such mistakes result in artifacts in the reconstructed foreground signal. We developed a new algorithm that estimates background intensity in fluorescence microscopy images and does not produce artifacts on the borders of nuclei.

A putative N-BAR-domain protein is crucially required for the development of hyphae tip appressorium-like structure and its plant infection in Magnaporthe oryzae

Membrane remodeling modulates many biological processes. The binding of peripheral proteins to lipid membranes results in membrane invaginations and protrusions, which regulate essential intra-cellular membrane and extra-cellular trafficking events. Proteins that bind and re-shape bio-membranes have been identified and extensively investigated. The Bin/Amphiphysin/Rvs (BAR) domain proteins are crescent-shape and play a conserved role in tubulation and sculpturing of cell membranes. We deployed targeted gene replacement technique to functionally characterize two hypothetical proteins (MoBar-A and MoBar-B) containing unitary N-BAR domain in Magnaporthe oryzae. The results obtained from phenotypic examinations showed that MoBAR-A deletion exerted a significant reduction in the growth of the defective ∆Mobar-A strain. Also, MoBAR-A disruption exclusively compromised hyphae-mediated infection. Additionally, the targeted replacement of MoBAR-A suppressed the expression of genes associated with the formation of hyphae tip appressorium-like structure in M. oryzae. Furthermore, single as well as combined deletion of MoBAR-A and MoBAR-B down-regulated the expression of nine different membrane-associated genes. From these results, we inferred that MoBAR-A plays a key and unique role in the pathogenesis of M. oryzae through direct or indirect regulation of the development of appressorium-like structures developed by hyphae tip. Taken together, these results provide unique insights into the direct contribution of the N-BAR domain proteins to morphological, reproduction, and infectious development of M. oryzae.