Modulation of the Binding Affinity of Polyzwitterion-Conjugated Protein by Ion-Specific Effects in Crowded Environments

Macromolecular crowding could influence the binding affinity of the polyzwitterion-conjugated proteins. Herein, the hydrolysis of N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide by the poly(carboxybetaine) conjugated α-chymotrypsin (PCT) was employed as a model system to investigate the modulation of the binding affinity of the polyzwitterion-conjugated proteins by the ion-specific effects in the crowded environments. In comparison with the bare α-chymotrypsin (BCT), the binding affinity of the PCT to the peptide is stronger in the dilute solutions but becomes weaker in the crowded environments. Our study demonstrates that the kosmotropic Ac– anion is incapable of achieving a stronger enzymatic binding affinity of the PCT than the BCT in the highly crowded environments. By contrast, the binding affinity of the PCT can be enhanced to be stronger than that of the BCT by the chaotropic SCN– anion in the crowded environments.