Binding interactions between pepsin and 3,3′,4,4′,5-pentachlorobiphenyl

One member of the polychlorinated biphenyls that is linked to a number of human diseases is 3,3 ',4,4 ',5-pentachlorobiphenyl. Here, density functional theory calculation, molecular simulations and multi-spectroscopic techniques were utilized to evaluate the interaction mechanism of 3,3 ',4,4 ',5-pentachlorobiphenyl with the pepsin, the digestive enzyme. The results of density functional theory and molecular simulations demonstrated that 3,3 ',4,4 ',5-pentachlorobiphenyl could be a good candidate for its availability toward pepsin with a frontier orbital gap of 0.18109 eV, and bound to the hydrophobic cavity of pepsin. The steady-state fluorescence and time-resolved fluorescence revealed that the quenching was initiated by complexation of pepsin and 3,3 ',4,4 ',5-pentachlorobiphenyl with the binding constant of 10(5) order. The UV-absorption, synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, and three-dimensional fluorescence data further confirmed that the changes in the secondary structure of pepsin were induced on the presence of 3,3 ',4,4 ',5-pentachlorobiphenyl, and a quantitative analysis of the secondary structure elements in pepsin was obtained.