Adaptation of Cell Membrane of Extremophiles

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Extremophiles belong to a class of living species that survive and thrive in some extreme conditions of this planet, such as extreme cold, high temperature, large pressure, high salinity, etc., which are not hospitable for life. Many of these conditions induce phase transformation of the lipid membrane, a major component of the cell membrane. Lipid membrane is a two-dimensional fluid and various functions of the cell membrane necessitate an appropriate fluidity of the lipid membrane. The fluid-to-gel phase transition due to various environmental stress factors disrupts various functionalities of the cell membrane. To combat the environmental stress factors these organisms adopt several strategies to protect their cell membrane. Homeoviscous adaptation is one such strategy that prevents the fluid-to-gel phase transition of the lipid membrane by fine-tuning the lipid composition to retain the fluidity of the membrane.  Another strategy to prevent fluid-to-gel phase transition is to introduce osmolytes, like urea, Trimethylamine N-oxide, sugars, etc. We focuses on the mechanism of the adaptation of the lipid membrane of some extremophiles

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Low Temperature Adaptation

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High Pressure Adaptation

Translational Jump-Diffusion of Supercooled Water

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We have developed a new approach to understand the dynamical anomalies in supercooled water and aqueous solutions, such as the breakdown of the celebrated Stokes-Einstein (SE) relation, which accounts for the coupling between translational self-diffusion and medium viscosity. The above breakdown has been quantitatively explained by the translational jump-diffusion (TJD) approach. The jump-diffusion coefficient — emanating from jump translation of water molecules — was calculated using a quantitative method. We observed that the jump-diffusion plays the major role in the breakdown of SE relation in supercooled water since the residual diffusion coefficient, the left-out component after separating out the jump-diffusion from total diffusion, remains strongly coupled to the medium viscosity. This novel TJD approach has been successful in explaining nonhydrodynamic behavior in some other systems, such as binary mixture of water and monohydroxy alcohol, vehicular diffusion of hydroxide ion in anion exchange membrane, water in confinement, etc. This approach has enormous potential in elucidating anomalous translational diffusion in complex chemical and biological systems.

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                  Understanding the dynamic heterogeneity of raft membrane 

Lipid rafts are nanoscopic domains of size ~10-100 nm enriched in saturated lipids having high melting point. These are assumed to be local reaction centers for protein clustering and activations. The raft structure is also thought to result in anomalous non-Brownian type diffusion of membrane proteins and lipids. The depiction of the spatio-temporal features of lipid raft domains is therefore key to understand the structure-function relationship of cell membrane. While experiments using different microscopic techniques are continuously contributing to the understanding of how lipids diffuse laterally across various nanodomains (raft) in microsecond to millisecond timescale, simulation (all atom or CG) studies does not contribute significantly except a very few reports.
 

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Modeled raft system 

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              Discotic liquid crystal on the water-vapour interface

We simulate discotic liquid crystal molecules on the water-vapour interface and study various physical properties. These works are done in a close collaboration with experimental work. We predict properties, such as e surface pressure (π) - area per molecule isotherms, orientation of molecules, and their strength of hydrogen bonding. Understanding the intermolecular interactions governing self-assembly is important to engineer molecular packing that controls the charge transport in discotic liquid crystal-based organic electronics

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                       Molecular Dynamics Simulation Group
                         
 We try to think like a molecule