Biology subjects

Tripathy, M.

Publications and source records attributed to Tripathy, M..

5 recordsLinked to original sources

bioRxiv2022

Using Packing Defects in Heterogeneous Biological Membrane as a Lens to Explore Protein Localization Propensity and Small Molecule Permeability

Plasma membrane (PM) heterogeneity has long been implicated in various cellular functions. However, mechanistic principles governing functional regulations of lipid environment is not well understood due to the inherent complexities associated with the relevant length and time scales that limit both direct experimental measurements and their interpretation. In this context, computer simulation holds immense potential to investigate molecular-level interactions that lead to PM heterogeneity and the related functions. Herein, we investigate spatial and dynamic heterogeneity in model membranes with coexisting liquid ordered and liquid disordered phases and characterize the membrane order in terms of the topological changes in lipid local environment using the non-affine parameter (NAP) frame-work. Furthermore, we probe the packing defects in membrane with coexisting fluid phases, which can be considered as the conjugate of membrane order assessed in terms of the NAP. In doing so, we formalize the connection between membrane packing and local membrane order and use that to explore the mechanistic principles behind preferential localization of proteins in mixed phase membranes and membrane permeability of small molecules. Our observations suggest that heterogeneity in mixed phase membranes follow some generic features, where functions may arise based on packing-related basic design principles. SignificanceFunctionally important complex lateral and transverse structures in biological membrane result from the differential molecular interactions among a rich variety of lipids and other building blocks. The nature of molecular packing in membrane is a manifestation of these interactions. In this work, using some of the ideas from the Physics of amorphous materials and glasses, we quantify the correlation between heterogeneous membrane organization and the three dimensional packing defects. Subsequently, we investigate the packing-based molecular design-level features that drive preferential localization of peptides in heterogeneous membrane and membrane permeation of small molecules.

biophysics↗

bioRxiv2022

Protein as evolvable functionally-constrained amorphous matter

We explore current ideas around the representation of a protein as an amorphous material, in turn represented by an abstract graph [G] with edges weighted by elastic stiffnesses. By embedding this graph in physical space, we can map every graph to a spectrum of conformational fluctuations and responses (as a result of say, ligand-binding). This sets up a "genotype-phenotype" map, which we use to evolve the amorphous material to select for fitness. Using this, we study the emergence of allosteric interaction, hinge joint, crack formation and a slide bolt in functional proteins such as Adenylate kinase, HSP90, Calmodulin and GPCR proteins. We find that these emergent features are associated with specific geometries and mode spectra of floppy or liquid-like regions. Our analysis provides insight into understanding the architectural demands on a protein that enable a prescribed function and its stability to mutations.

biophysics↗

bioRxiv2021

How does temperature affect the dynamics of SARS-CoV-2 M proteins? Insights from Molecular Dynamics Simulations

Enveloped viruses, in general, have several transmembrane proteins and glycoproteins, which assist the virus in entry and attachment onto the host cells. These proteins also play a significant role in determining the shape and size of the newly formed virus particles. The lipid membrane and the embedded proteins affect each other in non-trivial ways during the course of the viral life cycle. Unravelling the nature of the protein-protein and protein-lipid interactions, under various environmental and physiological conditions, could therefore prove to be crucial in development of therapeutics. Here, we study the M protein of SARS-CoV-2 to understand the effect of temperature on the properties of the protein-membrane system. The membrane embedded dimeric M proteins were studied using atomistic and coarse-grained molecular dynamics simulations at temperatures ranging between 10 and 50 {degrees}C. While temperature induced fluctuations should be monotonic, we observe a steady rise in the protein dynamics up to 40 {degrees}C, beyond which it surprisingly reverts back to the low temperature behaviour. Detailed investigation reveals disordering of the membrane lipids in the presence of the protein, which induces additional curvature around the transmembrane region. Coarse-grained simulations indicate temperature dependent aggregation of M protein dimers. Our study clearly indicates that the dynamics of membrane lipids and integral M protein of SARS-CoV-2 enables it to better associate and aggregate only at a certain temperature range (i.e., ~30 to 40 {degrees}C). This can have important implications in the protein aggregation and subsequent viral budding/fission processes.

biophysics↗

bioRxiv2019

Identifying Lipid Membrane Packing Defects in 3-Dimension: When Depth Does Matter

Lipid membrane packing defects are considered as essential parameter that regulates specific membrane binding of several peripheral proteins. In absence of direct experimental characterization, lipid packing defects and their role in the binding of peripheral proteins are generally investigated through computational studies, which have been immensely successful in unraveling the key steps of the membrane-binding process. However, packing defects are calculated using 2-dimensional projections and the crucial information on their depths is generally overlooked. Here we present a simple yet computationally efficient algorithm, which identifies these defects in 3-dimensions. We employ the algorithm to understand the nature of packing defects in flat bilayer membranes exhibiting liquid-ordered (Lo), liquid-disordered (Ld) and co-existing Lo/Ld phases. Our results indicate the presence of shallower and smaller defects in the Lo phase membranes as compared to the defects in Ld and mixed Lo/Ld phase membranes. Such analyses can elucidate the molecular scale mechanisms that drive the preferential localization of certain proteins to either of the liquid phases or their interface. Moreover, on the methodology front, our analyses suggest that the projection based 2-dimensional calculation of packing defects might result in inaccurate quantification of their sizes - a very important feature for membrane association of protein motifs, thus advocating the importance of the 3-dimensional calculations.

biophysics↗

bioRxiv2017

Using Topological Rearrangements to Characterize De-mixed Liquid Phases in Bio-membranes

Lateral heterogeneities in biomembranes play a crucial role in various physiological functions of the cell. Such heterogeneities lead to demixing of lipid constituents and formation of distinct liquid domains in the membrane. We study lateral heterogeneities in terms of topological rearrangements of lipids to identify the liquid-liquid phase coexistence in model membranes. By quantifying the degree of non-affine deformation associated with individual lipid, we are able to characterize the liquid ordered (Lo) and liquid disordered (Ld) phases in model lipid bilayers, without any prior knowledge about the chemical identity of the lipids. We explore the usage of this method on all atom and coarse-grained lipid bilayer trajectories. This method is helpful in defining the instantaneous Lo-Ld domain boundaries in complex multi-component bilayer systems.\n\nThe characterization is also used to highlight the effect of line-active molecules on the phase boundaries and domain mixing. Overall, we propose a framework to explore the molecular origin of spatial and dynamical heterogeneity in biomembrane systems, which can be exploited not only in computer simulations but also in experiments.

biophysics↗