Electrostatic interactions of enzymes in non-aqueous conditions: insights from molecular dynamics simulations.

Electrostatic interactions of enzymes and their effects on enzyme activity and stability are poorly understood in non-aqueous conditions. Here, we investigate the contribution of the electrostatic interactions on the stability and activity of enzymes in the non-aqueous environment using molecular dynamics simulations. Lipase was selected as active and lysozyme as inactive model enzymes in non-aqueous media. Hexane was used as a common non-aqueous solvent model. In agreement with the previous experiments, simulations show that lysozyme has more structural instabilities than lipase in hexane. The number of hydrogen bonds and salt bridges of both enzymes is dramatically increased in hexane. In contrast to the other opinions, we show that the increase of the electrostatic interactions in non-aqueous media is not so favorable for enzymatic function and stability. In this condition, the newly formed hydrogen bonds and salt bridges can partially denature the local structure of the enzymes. For lysozyme, the changes in electrostatic interactions occur in all domains including the active site cleft, which leads to enzyme inactivation and destabilization. Interestingly, most of the changes in electrostatic interactions of lipase occur far from the active site regions. Therefore, the active site entrance regions remain functional in hexane. The results of this study reveal how the changes in electrostatic interactions can affect enzyme stability and activity in non-aqueous conditions. Moreover, we show for the first time how some enzymes, such as lipase, remain active in a non-aqueous environment.Communicated by Ramaswamy H. Sarma.

Supercritical CO2/Deep Eutectic Solvent Biphasic System as a New Green and Sustainable Solvent System for Different Applications: Insights from Molecular Dynamics Simulations.

Deep eutectic solvents (DESs) are one of the most interesting research subjects in green chemistry nowadays. Due to their low toxicity, simple synthesis, and lower prices, they have gradually taken the place of other green solvents such as ionic liquids (ILs) in sustainable processes. However, problems such as high viscosity and high polarity limit the applications of DESs in areas such as extraction, catalysis, and biocatalysis. In this work, we introduce and evaluate the potential application of scCO2/DES for the first time. Molecular dynamics simulations were used to examine the phase behavior, polarity, molecular mobilities, and microstructure of this system. Results show that CO2 molecules can significantly diffuse to the DES phase, while DES components do not appear in the scCO2 phase. The diffused CO2 molecules significantly enhanced the molecular mobility of the DES components. The presence of CO2 molecules changes the DES polarity so that hexane can be solubilized and dispersed in the DES phase. Radial distribution functions show that the solubilized CO2 molecules have negligible effects on the microstructure of DES. It was shown that chloride and urea are the main interaction sites of CO2 in DES. The results of this study show that scCO2/DES as a new class of green and versatile solvents can open a new promising window for research in sustainable chemistry and engineering.

Study of alpha-amylase and gold nanoparticles interaction at two different temperatures through molecular dynamics.

The interaction of alpha-amylase with gold nanoparticles was studied at the two different temperatures of 25 and 75 °C through molecular dynamics simulation. To this end, 3-nm diameter spherical gold nanoparticles were designed. According to root mean square deviation results, at a high temperature, enzyme stability decreased in the absence of nanoparticles and increased in the presence of nanoparticles. Root mean square fluctuation results obtained for alpha-amylase residues indicated that the flexibility of residues 150-160 was affected more by the temperature in the presence and absence of nanoparticles. In addition, loop and helix regions in the secondary structure were affected more by the temperature. Results of enzyme contact maps in the designed systems showed that, in the absence of nanoparticles, a great number of contacts between residues were removed at high temperatures. The radius of gyration showed that the contact between the residues of amylase were removed in the absence of nanoparticles due to the enzyme expansion. Also Molecular dynamics simulation of α-amylase was performed in the presence of fifty 3- to 7-carbon sugar molecules at 25 and 75 °C. The results showed that the structure of α-amylase beta sheets is not affected by sugars. Docking of 3- to 7-carbon sugars with amylase sampled from simulations revealed that the affinity of sugars to the enzyme decreased at high temperatures in the absence of nanoparticles, while the presence of nanoparticles increased the affinity. Docking also showed that van der Waals and hydrophobic interactions contributed more than hydrogen interactions to the sugars-amylase interactions.

Does high pressure have any effect on the structure of alpha amylase and its ability to binding to the oligosaccharides having 3-7 residues? Molecular dynamics study.

Studies have shown that deletion of amino acids from the C-terminus of amylase do not alter its amylolytic activity. Although high pressure is used to modify the structure and function of this enzyme, the effects of high pressures on the structures of the wild-type and truncated amylases have not yet been understood at the molecular level. Using molecular dynamic simulations and docking, we studied the structures of wild-type and truncated Taka-amylases at high pressures (1000-4000 bar). To construct the truncated Taka-amylase, 50 and 100 C-terminal residues were removed in two separate steps. Results of simulation showed that, although the overall shape partly agglomerates with rise in pressure, high pressure fails to modify the structure of the barrel-like region of the ß-sheet in the wild-type and truncated enzymes. A comparison of contact graphs revealed that the changes at the N-terminus were less extensive than those at the C-terminus. Further analysis showed that 10 regions of the secondary structures changed due to pressure change in wild-type amylase, of which 6 regions were associated with the loops and 4 with helix, while the structure of ß-sheets remained unchanged. The docking of maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose with the averaged structures obtained from different simulations was conducted to characterize the influence of pressure on the activities of the wild-type and truncated enzymes. The results showed that maltoheptaose made hydrophobic contacts with residues Tyr238-Asp117-Tyr82-Leu166-Leu232-Tyr155 and hydrogen contacts with residues Asp233-Gly234-Asp206-Arg204-His296-Glu230. Similar results were obtained for other malto-oligosaccharides.