Study on the Interaction Mechanism of Methoxy Polyethylene Glycol Maleimide with Sweet Potato β-Amylase

Abstract

In this study, sweet potato β-amylase (SPA) was modified by methoxy polyethylene glycol maleimide (molecular weight 5000, Mal-mPEG5000) to obtain the Mal-mPEG5000-SPA modified β-amylase and the interaction mechanism between SPA and Mal-mPEG5000 was investigated. the changes in the functional groups of different amide bands and modifications in the secondary structure of enzyme protein were analyzed using infrared spectroscopy and circular dichroism spectroscopy. The addition of Mal-mPEG5000 transformed the random curl in the SPA secondary structure into a helix structure, forming a folded structure. The Mal-mPEG5000 improved the thermal stability of SPA and protected the structure of the protein from breaking by the surrounding. The thermodynamic analysis further implied that the intermolecular forces between SPA and Mal-mPEG5000 were hydrophobic interactions and hydrogen bonds due to the positive values of ΔHθ and ΔSθ. Furthermore, the calorie titration data showed that the binding stoichiometry for the complexation of Mal-mPEG5000 to SPA was 1.26, and the binding constant was 1.256 × 107 mol/L. The binding reaction resulted from negative enthalpy, indicating that the interaction of SPA and Mal-mPEG5000 was induced by the van der Waals force and hydrogen bonding. The UV results showed the formation of non-luminescent material during the interaction, the Fluorescence results confirmed that the mechanism between SPA and Mal-mPEG5000 was static quenching. According to the fluorescence quenching measurement, the binding constant (KA) values were 4.65 × 104 L·mol−1 (298K), 5.56 × 104 L·mol−1 (308K), and 6.91 × 104 L·mol−1 (318K), respectively.

Control of polymer–protein interactions by tuning the composition and length of polymer chains

“…Relevant discussions regarding the preferential interactions between organic monomers and protein amino acids are still lacking, primarily due to the lack of well resolved structures of polymer-antigen conjugates. 39 Preliminary results can be obtained for polyethylene glycol (PEG), 40,41 where the repeating ethylene glycol monomer has been revealed with the binding preference to aromatic amino acids in anti-PEG antibodies. 30 This result could be crucial for a more rational selection of functional monomers for polymer antibodies, according to the surface functionalities of the antigen protein.…”