17] Structure and lipid binding properties of serum albumin

Abstract

Bovine albumin is composed of a single polypeptide chain containing 581 amino acid residues, and there are many regions of homology in the amino acid sequence, and the polypeptide chain is folded into three similar globular domains, designated I, II, and III, composed of 185, 192, and 204 amino acid residues, respectively. This chapter describes the structure and lipid binding properties of serum albumin. The primary and secondary fatty acid binding sites are located between or within loops lined with hydrophobic amino acid side chains. Two methods have been employed to localize the binding sites within the albumin structure; one is fluorescence spectroscopy, and the other is proteolytic cleavage followed by equilibrium binding to the resulting protein fragments. Both methods of analysis indicate that the strongest fatty acid binding site is located within the third domain. The chapter indicates that fatty acid binding is associated with small conformational changes that allow the fatty acid to penetrate into the interior of the globular protein structure and enable the albumin binding sites to adapt to the configuration of the fatty acyl chain.