Characterization of Ligand Binding Sites on the a1-Acid Glycoprotein in Humans, Bovines and Dogs

The goal of this study was to classify and identify the ligand binding sites on a1-acid glycoprotein (AGP) from 3 species, in order to understand species diferences with respect to both ligand binding properties and ligand interaction on protein binding. These characteristics of human, dog and bovine AGP were examined using the basic ligands chlorpromazine and auramine O, the acidic ligand acenocoumarin, and the steroid hormone progesterone. Ultrâltration and fluorescence techniques were used to characterize the nature of the interactions, and the data were analyzed according to the method of Kragh-Hansen. Using a model analysis of the interaction, the ligand binding site on human AGP consists of at least 3 partially overlapping subsites: a basic ligand binding site, an acidic ligand binding site and a steroid hormone binding site. Moreover, dog and bovine AGP each have a basic ligand binding site and a steroid hormone binding site, which significantly overlap and aject each other. However, dog and bovine AGPs do not contain an acidic ligand binding region. The results of the fluorescence experiments indicate that the hydrophobic nature of the ligand binding pockets on the 3 AGPs are similar, but that their microviscosities are markedly diferent.