Effect of polymer molecular weight on chitosan–protein interaction

• Chitosan nanoparticles bind BSA and HSA via hydrophobic and electrostatic contacts.
• Chitosan forms more stable complexes with BSA than HSA.
• Increasing chitosan molecular weight improved the binding constant of the complexes. kDa.
• Larger chitosan nanoparticles induced more alterations of protein conformation.
• Complexation of chitosan and protein leads to polymer morphological changes.

We present a comprehensive study of the interactions between chitosan nanoparticles (15, 100 and 200 kDa with the same degree of deacetylation 90%) and two model proteins, i.e., bovine (BSA) and human serum albumins (HSA), with the aim of correlating chitosan molecular weight (Mw) and the binding affinity of these naturally occurring polymers to protein. The effect of chitosan on the protein secondary structure and the influence of protein complexation on the shape of chitosan nanoparticles are discussed. A combination of multiple spectroscopic methods, transmission electron microscopy (TEM) and thermodynamic analysis were used to assess the polymer–protein complex formation. Results revealed that the three chitosan nanoparticles interact with BSA to form chitosan-BSA complexes, mainly through hydrophobic contacts with the affinity order: 200 > 100 > 15 kDa. However, HSA-chitosan complexation is mainly via electrostatic interactions with the stability order: 100 > 200 > 15 kDa. Furthermore, the association between polymer and protein causes a partial protein conformational change by a major reduction of α-helix from 63% (free BSA) to 57% (chitosan-BSA) and 57% (free HSA) to 51% (chitosan-HSA). Finally, TEM micrographs clearly revealed that the binding of serum albumins with chitosan nanoparticles induces a significant change in protein morphology and the shape of the polymer.

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