Study Of Amino Acid Synergism In The Inhibition Of Methane Hydrate Growth By Type Ⅰ Antifreeze Protein

Natural gas hydrates are solid molecules that are captured into hydrogen bonded cage like networks under thermodynamic favorable conditions.Due to the fact that the guest molecules typically captured are methane molecules,natural gas hydrates are commonly referred to as methane hydrates.The accidental formation of hydrates in pipelines and processing equipment is a serious problem in the oil and gas industry.Many organisms that living in cold environment have a kind of protein that can inhibit the growth of ice crystals.These proteins can inhibit the growth and recrystallization of ice crystals by generating thermal hysteresis activity,thereby enabling organisms to survive in low-temperature environments.These proteins are called antifreeze proteins(AFPs).The research shows that antifreeze proteins is an effective inhibitor of natural gas hydrate growth and nucleation.However,the detailed mechanism of antifreeze proteins inhibiting the growth of natural gas hydrate is still unclear.This article adopts the method of all atom dynamics simulation to study the details of the binding between type Ⅰ antifreeze protein(AFPI)and methane hydrate at the molecular level.The method of amino acid mutation was used to simulate AFPI and analyze the adsorption and binding process of AFPI and its mutants with methane hydrates in low temperature and high-pressure environments.The simulation results indicate that AFPI is an effective inhibitor of natural gas hydrate growth.The simulated data of mutant antifreeze proteins showed that the amino acid mutant antifreeze proteins also had the ability to inhibit the growth of methane hydrate.At the same time,the spatial structural changes of protein amino acid residues during the binding process of AFPⅠ were observed.The data of protein mutation comparison experiment showed that the structural change of AFPⅠ in the process of combining antifreeze proteins with hydrate occurred expansion and folding,which led to the migration of methyl groups of some amino acid residues at HBS to adapt to the cage structure of hydrate and replaced methane molecules to combine with the hydrate surface.In addition,mutant simulation showed that the deletion of methyl group on AFPⅠ side chain would inhibit the binding ability of antifreeze proteins to hydrate.During the process of binding AFP I to the surface of hydrates,structural changes occur in protein molecules,causing the protein surface to complement the surface of hydrates,thereby stably binding to the surface of hydrates and inhibiting the growth of hydrates.