A Haloalkane Dehalogenase DhaA Nanoparticle Based on Pullulan Conjugation and Polyethyleneimine Adsorption

Haloalkane dehalogenase DhaA is a member of the α/β-hydrolase superfamily and can degrade the halogenated compounds. However, the enzyme could not tolerate harsh and extreme environmental conditions, such as high temperature, extreme pH, and hypersaline, which limits its practical applications. Pullulan is a hydrophilic polysaccharide and acts as an additive to improve the enzyme stability. Polyethyleneimine (PEI) is a protein stabilizer and a polymer with a high density of ionizable amino groups. In the present study, DhaA was covalently conjugated with acetylated pullulan and adsorbed with PEI by electrostatic interactions to form nanoparticles (PEI-pullulan-DhaA). As compared with DhaA, PEI-pullulan-DhaA essentially maintained the enzymatic activity of DhaA, along with slight change in the kinetic parameters and enzyme conformation. The conjugated pullulan tends to form a large hydrated layer around DhaA. PEI, a cationic polymer, generated an amphiphilic microenvironment around DhaA. Pullulan conjugation and PEI adsorption could significantly improve the stability of DhaA against high temperature and low pH by structural stabilization of DhaA. PEI-pullulan-DhaA could also tolerate the hypersaline, organic solvents, and long-term storage. Thus, PEI-pullulan-DhaA has a strong environmental stability and is promising for industrial and environmental applications.