Binding to Bovine Serum Albumin: Effects of Molecular Structure

Abstract

Bovine Serum Albumin (BSA) is a model protein which has been used to investigate interactions between proteins and other substances. Prior work has shown that serum albumin plays a significant role in the body as a transport protein moving a broad range of substances through the bloodstream. The binding of different compounds such as rose Bengal (RB), methylene blue (MB) and avobenzone to BSA was studied using fluorescence spectroscopy. The fluorescence of BSA is primarily dependent upon tryptophan; therefore, if the binding to the protein is localized near a tryptophan residue, the fluorescence signal will be diminished (known as quenching). BSA is known to have two binding sites, site I and site II. A tryptophan residue is present in site I so the degree of quenching for compounds bound to site I should be greater than that of compounds bound to site II. The shape, size, and polarity of sites I and II are unique accounting for the different binding specificities, and allows for testing the hypothesis relating the molecular structure of the bound molecule to its preferred binding site. Our data indicate that RB binds strongly to BSA site I and MB binds to BSA site II. The data for avobenzone suggests a similarity with that of MB; we therefore assume that it also resides in site II. For further studies, we will use the structural properties of various compounds to predict the site on BSA they will be bound to and verify our hypothesis