Effect of temperature and dehydrating conditions in Taridgrade specific secreted abundant heat-soluble class proteins: An atomistic molecular dynamics simulation study

Abhijith, E. K. (2019) Effect of temperature and dehydrating conditions in Taridgrade specific secreted abundant heat-soluble class proteins: An atomistic molecular dynamics simulation study. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Tardigrades are known to survive in a wide variety of extreme environments. They express unique stress adaptation mechanisms which allows them to endure extremes of temperature, radiation, pressure, and even vacuum. Studies have shown that these micro animals are able to endure almost complete desiccation through transition to a metabolically inactive state, known as anhydrobiosis. Initial investigations in to desiccation tolerance identified the disaccharide trehalose as primary agent of anhydrobiosis. Trehalose amasses in high concentration in many anhydrobiotic organisms upon exposure to desiccating conditions. Recent studies have found out that the build-up of trehalose was much less in tardigrades, varying from 0% to 2.9% of the total body weight (less than 1% in some tardigrade species) which indicates that tardigrades have other factors to tolerate dehydration. Recently a group of scientists have discovered the crucial proteins present in tardigrades which helps them to transition between metabolically active and inactive state depending on the level of water content. These key proteins are coined as “Tardigrade-specific Intrinsically Disordered Protein” (TDPs). There are presently three classes of IDPs identified: - Cytosolic abundant heat soluble (CAHS) protein, Secreted abundant heat soluble (SAHS) protein, Mitochondrial abundant heat soluble (MAHS) protein all named based on the region in which they get localized in large concentrations on desiccation inducing conditions. The mechanism through which these TDPs protect the Tardigrades from extreme stresses are not clearly known. Till now there are two crystal structure of TDPs identified, both from the SAHS protein family. The overall objective of the present work is to investigate the structural rearrangements of the SAHS1 protein in response to temperature and other dehydrating conditions using atomistic molecular dynamics (MD) simulations. Simulations studies on SAHS1 protein dimer at varying temperature so far indicates that absence of Zn²⁺ linkage between monomers destabilizes the dimer structure. Few experimental studies suggest that SAHS1 protein undergo a beta-strand to alpha helical transition on solvating with trifluoroethanol (mimicking a water deficient condition). The preliminary results from the simulation studies done on SAHS1 monomer at varying concentrations of trifluoroethanol also indicates the same.

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