Insights into cyclodextrin-modulated interactions between protein and surfactant at specific and nonspecific binding stages

Cyclodextrin (CD) modulated interactions between ionic surfactants with opposite charge and bovine serum albumin (BSA) at specific and nonspecific binding stages have been studied by isothermal titration calorimetry (ITC), fluorescence spectra and circular dichroism spectral measurements. At the specific binding stage with high affinity, the effectiveness of both α- and β-CD for hindering BSA–SDS interactions is quite weak; however, CD is more effective in hindering BSA–CTAB specific interactions. This is due to the cooperative electrostatic and hydrophobic interaction between BSA and SDS, and to the absence of the cooperative interaction between BSA and CTAB at the specific binding stage. For both BSA–SDS and BSA–CTAB systems (especially in the former system), α-CD is more effective in hindering BSA–surfactant interactions than β-CD. At the nonspecific binding stage, the addition of both α- and β-CD can hinder totally both BSA–SDS and BSA–CTAB hydrophobic interactions. This is caused by the more specific hydrophobic interaction between CD and surfactant compared with the hydrophobic interaction between BSA and surfactant. Our results show that the CD effect on the protein–surfactant interaction depends on both the nature of the protein–surfactant interaction and the complexing ability of CD with surfactant.

Illustration of the mechanism for modulating the specific interaction between BSA and surfactant by cyclodextrin, (A) BSA–SDS, (B) BSA–CTAB.Figure optionsDownload high-quality image (118 K)Download as PowerPoint slideResearch highlights
► CD has different effect on protein-surfactant specific and nonspecific interaction.
► CD effect depends on the nature of the protein–surfactant specific interaction.
► Cooperative interaction between BSA and SDS is hard to inhibit by CD.
► CD effect depends also on CD–surfactant (with linear tail) association constant.