Characterization of bovine serum albumin–tryptophan interaction by capillary isoelectric focusing with whole column imaging detection

Capillary isoelectric focusing (cIEF) with whole column imaging detection (WCID) was explored for the characterization of bovine serum albumin (BSA)–tryptophan interaction, to further understand protein–drug interactions. The BSA–tryptophan interaction was dynamically monitored by cIEF–WCID, to provide the cIEF profiles of the BSA–tryptophan interaction system at different focusing times. Our study demonstrated that the cIEF behavior of BSA can serve as a probe into the study of BSA–tryptophan interaction, through monitoring the change in its cIEF profile when the interaction occurred. The study illustrated that the BSA peak split due to the BSA–tryptophan interaction, and the peak of BSA–tryptophan complex was clearly identified in the cIEF electropherograms. By comparing the cIEF profiles of BSA/l-tryptophan and BSA/d-tryptophan, respectively, our study demonstrated that BSA interacted with the enantiomers of tryptophan with a chiral recognition. l-Tryptophan demonstrated a very strong interaction with BSA, while d-tryptophan exhibited a much weaker interaction with BSA. The effects of the BSA concentration, the tryptophan concentration, the focusing time and the incubation time on the BSA–tryptophan interaction were investigated. This study offers a novel approach for the study of protein–drug interactions.