The Molecular Dynamics Simulation Of ELPs Phase Transition And Its Interaction With Xylanase

Elastin-like polypeptides are geting more and more attention for its reversiblephase transition. This paper focus on a new kind of elastin-like polypeptides (ELP[KV8F-20]), which is reported as the shortest ELPs tag, and more sensitive to saltconcentration. When elastin-like polypeptides are heated above the lower criticalsolution temperature, there will be a reversible and sharp phase transition. Thisbehavior is retain when ELPs are fused to a soluble protein, and it provide achromatography-less method for isolating a recombinant ELP fusion protein. Bycycling the solution through the soluble and insoluble phase, the fused protein wouldbe able to be isolated. This method (Inverse Transition Cycling, ITC) can significantlyreduce the cost of protein purification and it would be easily to scale up.This paper focus on three issues:1. ELPs are sensitive with different kinds of saltsolution, especially different anion, but here is currently no clear explanation for thisphenomenon.2. Longer ELPs get lower critical temperature, which means longerELPs is more sensitive to the salt concentration, while this phenomenon reminded noexplanation either.3. When ELPs[KV8F-20] is fused to xylanase, we found that oncethe fused protein gets insoluble, it will be hard for it to be soluble again.To answer these questions, this research has three parts: The molecular dynamicssimulation of ELPs [KV8F-20], The molecular dynamics simulation ofELPs[KV8F-40], and The molecular dynamics simulation of ELPs with xylanase.The result of molecular dynamics simulation shows that the β-spiral ofelastin-like polypeptides are unstable in the solvate compared to other proteins.During the molecular dynamics simulation process, the β-spiral structure wasdestroyed in6nano seconds. The structure of β-spiral of ELPs is found in the crystalof ELPs, and molecular dynamics simulation shows that this structure is totallydifferent from the structure of soluble ELPs. ELPs trend to have a structure of randomcoil rather than β-spiral when it is soluble, β-spiral only exist in the state of insoluble.We focus on the structure change of ELPs solvating to find the mechanism of thereversible phase transition of ELPs.Molecular dynamics simulation shows that the amounts of hydrogen bonds areconnected to the reversible phase transition of ELPs. When the temperature isincreased by25K, it would result in the loss of6%~10%hydrogen bonds. The carbonate solution gets1.2%(400K)~5.2%(300K) hydrogen bonds more thanchloride ion, and this difference is connected to the temperature of the simulation. Inthe carbonate solution, the0.1mol/L incensement of the concentration resulted in theincrease of1%~2%. The carbonate helps ELPs to build hydrogen bonds.ELPs[KV8F-40] get75%~85%more hydrogen bonds than ELPs[KV8F-20], sothey are more sensitive to ion concentration. Longer sequence of amino acid helps tobuild more hydrogen bonds on one ELPs molecule. It will be more possible forELPs[KV8F-40] to build hydrogen bonds with other molecules compared withELPs[KV8F-20]. The result of molecular dynamics simulation shows the β-spiral inELPs[KV8F-40] is more stable than ELPs[KV8F-20]. The β-spiral structure turns outto be the structure of insoluble ELPs.The result of molecular dynamics simulation shows that ELPs20can build1~5hydrogen bonds when interacting with xylanase, it helps to keep the original structureof ELPs20. When interacting with xylanase, the structure of ELPs20is more stablethan ELPs40. Fewer hydrogen bonds were built with solution because xylanasecompete to build hydrogen bonds with ELPs. Therefore, the fused protein is lesssensitive to the concentration. The hydrogen bonds between fused proteins may be themain reason for the insoluble ELPs20-xylanase aggregates.