Interaction between linear PEGylated cationic block copolymers and human serum albumin

Interaction of proteins with synthetic polyelectrolytes is significant with respect to various biological applications. In this work, a detailed spectroscopic study of the binding between a series of PEGylated linear cationic block polymers (BCPs) and human serum albumin (HSA) at physiological pH has been carried out. Techniques like steady-state fluorescence spectroscopy, life-time measurements by time-correlated single photon counting (TCSPC) method and protein conformation analysis by circular dichroism (CD) measurements were employed at different temperatures. Analysis of the quenching data indicated a static quenching mechanism occurring during polymer-protein interaction. The electrostatic interaction between cationic tertiary ammonium groups of the BCPs and negatively charged amino acid residues present in HSA is the predominant force contributing to the binding process. On the other hand, the presence of PEG units in the BCPs significantly influenced the overall binding process. Conformational analysis of HSA using CD studies suggested that the linear PEG units resisted changes in the secondary structure of HSA to a significant extent, resulting in weakening of the overall binding of cationic BCPs and HSA. Detailed analysis of the thermodynamic parameters like ∆ G0, ∆ H0 and ∆ S0 indicated that the binding process was entropy driven spontaneous in nature.