An investigation of folic acid-protein association sites and the effect of this association on folic acid self-assembly.

The contribution of folic acid (FA)-tryptophan interactions to FA-protein association was investigated in the context of using FA as a drug carrier in protein delivery systems. Bovine serum albumin (BSA) and indolicidin were used as model proteins in the study. The FA-BSA complex was characterized by using the Bradford reagent to identify the impact of FA-BSA association on BSA-dye reagent interactions. UV-visible spectroscopic analysis of the FA-BSA mixture showed that the absorbance maximum of BSA-dye reagent occurred at 595 nm, even after the association of FA with BSA. This confirms that protonated amino acid groups of the protein are not involved in FA-BSA association. Moreover, molecular dynamics (MD) simulation confirmed the presence of an associative interaction between aromatic moieties in FA and tryptophan moieties in the indolicidin molecule, which disrupted FA self-assembly. An X-ray diffraction (XRD) study showed that there was limited disruption of FA self-assembly after the addition of BSA or tryptophan. This suggests that FA and BSA are compatible and associate with each other. Graphical Abstract Mechanism of folic acid and protein association.