Conformational change of lysozyme on the interaction with gene carrier polyethyleneimine

Polyethyleneimine (PEI) has been considered as "golden standard" for polymeric gene delivery carriers, however also induces cytotoxicity. To reveal the molecular basis of PEI cytotoxicity, absorption, resonance Rayleigh scattering, fluorescence, circular dichroism and isothermal titration calorimetry were conducted to investigate the interaction between PEI (average molecular weight 25,000 Da) and lysozyme and its influence on the conformation of the enzyme. PEI is an amphiphilic polymer with strong hydrogen bonding capability and weak hydrophobicity due to dense amine groups and methyl groups. However, the hydropathic characteristics that hydrophobic methyl groups and hydrophilic amine groups distributed alternatively along the polymer chain made it difficult to penetrate into the hydrophobic core, but subject to binding onto the surface of lysozyme via hydrophobic interaction and hydrogen bond, leading to a more compact conformation and an increased surface hydrophobicity of the enzyme.