Biochemical characterization of bovine lactoferrin as a glycyrrhizin-binding protein in vitro

Lactoferrin (LF) from bovine colostrum was biochemically characterized as a glycyrrhizin (GL)-binding protein (gbP) in vitro. It was found that (i) bovine LF (bLF) and a synthetic bovine lactoferricin (bLFcin, the N'-terminal region of bLF at the positions 17--41) had a high affinity to a GL-affinity column; (ii) approximately 1.8 moles of GL were bound to a molecule of bLF with a binding constant of approx. 1.20x10(4) M(-1) at pH 6.8; and (iii) GL, but not glycyrrhetinic acid (GA), induced a conformational change of bLF. In addition, the glucuronic acid moiety of the GL molecule was found to be responsible for binding to bLF, because (i) no binding of GA and two glucoses-GA (Glc-Glc-GA) to bLF was detected; and (ii) a synthetic fluorinated GL (GlcA-GlcF-GA) and mono-glucuronyl-GA (mono-GlcA-GA) were bound significantly to bLF. A similar binding of GL to human LF (hLF) was also observed under the same experimental conditions. Data provided here suggest that (i) bLF contains plural GL-binding sites; and (ii) the specific binding of GL to bLF may modulate the physiological activity of bLF in vivo.