Study On The Thermostability Of Cold Shock Protein Bc-Csp

The protein thermostability is a hotspot of protein researches. Proteins perform their function at a range of their growth temperature and excessively high or low temperature will make them denature and lose their function. How to enhance the thermostability of proteins to maintain theirs structure and function at the higher temperature is an unsolved problem in protein engineering. Studying the heat-resistant mechanism of thermophilic protein deeply is very significant for better understanding of protein folding, structure, function, evolution and other issuesIn this thesis, we mainly analyze the thermostability of cold shock protein Bc-Csp. The cold shock protein thermophile Bacillus caldolyticus (Bc-Csp) and its homologous protein mesophile Bacillus subtilis (Bs-CspB) are very similar in sequence and structure but they have great difference on thermostability. Researches have shown that only two surface-exposed residues are responsible for the increase in stability of the thermophilic protein although the two proteins differ in sequence at 12 positions.We develop a novel method which uses all-atom simulation to study the thermal stability of the protein and advance a hypothesis that the ion pairs don't affect the thermostability of proteins. Using our method, we calculate the thermostability differenceΔΔG, between 21 mutants of Bc-Csp and Bc-Csp. Our calculated results and experimental results have a good linear correlation. These results afford the assumption may be correct and the simulation method is reliable.Further, we carefully analyze the reason of the increased thermostability of Bc-Csp compare to its homologous protein Bs-CspB and attain similar results with the experimental study. The increasedΔΔG cal of E3R originates from two sources: one-third is van der Waals interaction and two-thirds gain from electrostatic interaction. The increasedΔΔG cal of E66L originates from van der Waals interactions. The A46E almost don't affect the thermostability although 46E form two additional ion pairs in Bc-Csp and the main reason is that the ion pairs don't affect the thermostability of proteins.