The Effect Of Temperature And Salt Solution On The Stability Of Protein Structure

Proteins are biological macromolecules and important carriers of biological functions.The relative molecular mass and spatial conformation are different for different proteins.The diversity of protein functions is determined by the complexity of protein molecular structure.The structural properties of proteins may be affected by complex and variable external environments such as salt solutions and temperature,and the biological activities of proteins will be changed accordingly.With further research,it is very difficult to obtain higher-dimensional kinetic information on protein structure and high-resolution structural data by experimental methods.The puzzle was solved using computer simulations.In this paper,the molecular dynamics（MD）simulation method is used to study the structural characteristics and dynamic behavior of different types of protein systems such as all-αand all-βproteins in different external environments（temperature,salt solution）.The main research contents in the paper are as follows:（1）The energy changes and structural stability of Escherichia coli hydrolipid amide dehydrogenase immersed in different salt solutions at different temperatures were studied based on the MD method.Four kinds of salt solutions,Ca Cl₂,Mg Cl₂,Na Cl,and KCl,were selected as salt solutions in our work to study their energy and structural changes.The maximum value of RG and RMSD are located at specific concentrations,indicating the loose structure of the protein when immersed in the salt solution with a certain concentration.Compared to the monovalent salt solution,the divalent salt solution has a lower concentration when the radius of gyration and root mean square deviation exhibits a maximum value,which is half the concentration of the monovalent salt solution.The RMSD deviation of the protein and the degree of freedom of the backbone Cαatoms increase with increasing temperature,indicating the protein stability at high temperature is weakened.The study also found that the electrostatic potential energy of the protein system increases with the increase of temperature and decreases with the increase of the solution concentration.The van der Waals energy is always opposite to the change of electrostatic potential energy,and the total potential energy of the system is always consistent with the changing trend of the electrostatic potential energy.（2）Two proteins,with the same amino acid sequence but different secondary configurations were constructed as all-αprotein and all-βprotein.The effect of environmental temperature and salt solutions on the structural transition of the two types of protein systems was studied by MD simulation.Two salt solutions,Ca Cl₂and Na Cl,were selected and added to the aqueous solutions of the two proteins to build different models.The changes in the potential energy and secondary structure of the system in the equilibrium state were analyzed.And the stability of the two proteins in the external environment was also revealed.The results show that theβ-sheet is looser and less stable than theα-helix structure.Theα-helix protein,as the same as 1BBL,the structural properties of the all-αprotein in the external environment,the changing trend of theβsheet is similar to that of theαhelix,and the change of theβsheet is much more severe.（3）The MD simulation method was used to analyze the structural stability and energy transition of the all-αproteins with different chain lengths in different external environments.All-αproteins composed of 26 alanine residues and 36alanine residues were constructed.Comparing these two proteins with the all-alpha protein in the research work（2）,which is also composed of 13 alanine residues,and analyzing the structural transition of the three-chain-length all-alpha protein system in the external environment.The change trends of the three proteins in the external environment such as temperature and salt solution are all the same through the analysis of the simulation results.The influence of the chain length on the radius of gyration of the protein is more obvious than that of the external environment,which is roughly positively correlated.The longer chain length,the looser structure the protein has.From the estimate for the root mean square deviation,the influence of the external environment on temperature and salt solutions is higher than that of the chain length.The larger root mean square deviation of the protein with a longer chain length at the same temperature,the weaker stability of the protein has.