The Thermo Stability of Lipase: Salt Bridge and Salt Bridge Network Perspective Based on Long Time Molecular Dynamics Simulation

Salt bridges (Sbs) play an important role in stabilizing protein. Long time molecular dynamics simulation was performed at different temperatures to study salt bridges dynamics and salt bridges networks of Wild Type Lipase (WTL) (Tm=56 °C)and mutant 6B(Tm=78.2 °C). The higher salt bridge persistence value generally means that the Sb is more stable. The persistence values of Lys35-Asp34, Glu171-Arg147 and Asn181-Lys122 in 6B are different from those of WTL with temperature increasing. The improvement on the stability of these Sbs show that they stabilize the protein secondary structure and then strengthen the ability of protein to withstand high temperature. In addition, the mutations A20E and G111D form new Sbs which affect the Sbs networks dynamics of 6B. Due to the mutations, it forms new small Sbs network and enhances the stability of two salt bridge networks. The first Sbs network makes αB, loop and 310-helix closely connect with each other at mutant. The second Sbs network improves the internal interaction of the αB. The third Sbs network enhances the interaction between loops, αD and αE. It is thus clear that the mutations change the stability of Sbs and the Sbs networks which is responsible for increasing thermostability of 6B.