Effects of p-sulfonatocalixarene and p-sulfonatocalixarene/sulfobetaine surfactant complex on the activities of bromelain and polyphenol oxidase

Calixarene is a third-generation supra-molecular compound and has broad application prospects in clinical disease diagnosis and intervention treatment. Calixarene/surfactant systems have received increasing attention recently because the properties of these systems can be customized. However, very little is currently known about the binding of calixarene and calixarene/surfactant systems to proteins and the effects of calixarene and calixarene/surfactant systems on protein activity. In this study, we studied the binding of sulfonatocalix[n]arene (SC[n], n = 4, 6 and 8) with bromelain (BM) and polyphenol oxidase (PPO) both in the absence and presence of sulfobetaine surfactant (N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SDDAB)) using various techniques, including protein activity measurements, molecular simulation, and fluorescence, UV–Vis, 1 H NMR, and circular dichroism spectroscopies. We found that SC[n] entered the docking pocket of the proteins in a stoichiometric molar ratio of 1:1, whereas the proteins did not enter the cavity of SC[n]. In addition, SC[n] formed a stronger bond with BM than with PPO. SC[n] decreased the activities of the proteins, where the activity of BM was inhibited to a greater extent than that of PPO. SC[n] and SDDAB formed complexes. The proteins did not destroy the binding between SC[n] and SDDAB but bonded with the SC[n]/SDDAB complex instead by interacting with SDDAB. Moreover, the protein activities could be controlled by the molar ratio of SC[n] to the surfactant: a lower ratio corresponded to higher activity.