Effects of different fatty acid ligands on the host-guest interaction of astaxanthin-bovine serum albumin: Thermodynamical analysis, binding site identification, and in vivo antioxidant evaluation

Abstract

The multi-ligand binding properties of proteins make the introduction of small-molecule ligands an effective approach through which to improve the biological functions of protein-based carriers. In this study, the effect of fatty acids (FAs) as functional ligands on the self-assembly of astaxanthin (ASTA) and bovine serum albumin (BSA) and the in vivo antioxidant properties of their ternary ligand complexes were investigated. As the seven common dietary FAs, lauric acid (LAA), palmitic acid (PA), stearic acid (SA), oleic acid (OA), linoleic acid (LA), arachidonic acid (AA) and docosahexaenoic acid (DHA) were selected. The results indicated that, with the exception of DHA, six of these FAs were able to change the conformation of BSA while simultaneously improving its hydrophilicity. The introduction of FA ligands did not affect the binding mode (static quenching) or the type of intermolecular forces (hydrogen bonding and van der Waals forces) between ASTA and BSA. However, the involvement of FA ligands could cause the dominant binding domain of ASTA in BSA to migrate from the initial subdomain IIIA (site II) to subdomain IIA (site I). Simultaneously, the altered binding affinity between ASTA and BSA was also observed, and the effect of unsaturated FAs (except DHA) was more pronounced than that of saturated ones. As expected, compared with the ASTA-BSA binary complexes, the ASTA-FA-BSA terpolymer performed an increased total antioxidant capacity in vivo as well as an improved antioxidant protein expression. This study provides a new strategy for the efficient delivery of carotenoids using proteins and function ligands. • Different FA ligands altered the conformation of BSA to different degrees. • The effect of different FA ligands on the hydrophilicity of BSA was variable. • The FA ligands did not affect the binding mode between astaxanthin and BSA. • The FA ligands changed the dominant binding domain of astaxanthin in BSA. • The FA ligands improved the in vivo anti-oxidative activity of astaxanthin.