Abstract
The conformational stability and activity of Candida antarctica lipase B (CALB) in the polar and nonpolar organic solvents were investigated by molecular dynamics and quantum mechanics/molecular mechanics simulations. The conformation change of CALB in the polar and nonpolar solvents was examined in two aspects: the overall conformation change of CALB and the conformation change of the active site. The simulation results show that the overall conformation of CALB is stable in the organic solvents. In the nonpolar solvents, the conformation of the active site keeps stable, whereas in the polar solvents, the solvent molecules reach into the active site and interact intensively with the active site. This interaction destroys the hydrogen bonding between Ser(105) and His(224). In the solvents, the activation energy of CALB and that of the active site region were further simulated by quantum mechanics/molecular mechanics simulation. The results indicate that the conformation change in the region of active sites is the main factor that influences the activity of CALB.
Highlights
Because of its high enantioselectivity and catalytic activity, wide range of substrates, and thermal stability, Candida antarctica lipase B (CALB)3 is widely used in many industrial applications and scientific researches [1]
The most widely accepted model was described by Laane [14], who summarized the influence of organic solvents on the enzymatic reactions and concluded that the enzyme activity is higher in the environment surrounded by nonpolar and midpolar solvents, whereas the lowest activity is expressed in polar solvents
The results of the conformation change of the active site indicate that the breakdown of the hydrogen bond between OG (Ser105) and NE2 (His224) leads to the low activity of CALB in the polar solvents, and the breakdown of the hydrogen bond is due to the intensive interaction between the active site and the polar solvent molecules
Summary
Because of its high enantioselectivity and catalytic activity, wide range of substrates, and thermal stability, Candida antarctica lipase B (CALB) is widely used in many industrial applications and scientific researches [1]. The most widely accepted model was described by Laane [14], who summarized the influence of organic solvents on the enzymatic reactions and concluded that the enzyme activity is higher in the environment surrounded by nonpolar and midpolar solvents, whereas the lowest activity is expressed in polar solvents. The Laane model does not describe the mechanisms of solvent effect on a molecular level. The overall conformational change of CALB and the local conformational change around the active site in polar and nonpolar organic solvents were investigated through molecular dynamics simulation. Through constructing the tetrahedral intermediate model, the solvent effect of the conformation change on the activity of CALB was investigated by quantum mechanics (QM)/molecular mechanics (MM) simulation
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