Comparison of the energetics of avidin, streptavidin, neutrAvidin, and anti-biotin antibody binding to biotinylated lipid bilayer examined by second-harmonic generation

A comparison of the binding properties of avidin, streptavidin, neutrAvidin, and antibiotin antibody to a biotinylated lipid bilayer was studied using second-harmonic generation. Protein binding assays were performed on a planar supported lipid bilayer of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) containing 4 mol % biotinylated-cap-1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (biotin-cap-DOPE). The equilibrium binding affinities of these biotin-protein interactions were determined, revealing the relative energetic contributions for each protein to the biotinylated lipid ligand. The results show that the binding affinities of avidin, streptavidin, and neutrAvidin for biotin were all strengthened by protein-protein interactions but that the stronger protein-protein interactions observed for streptavidin and neutrAvidin make their binding more energetically favorable. It was also shown that neutrAvidin has the highest degree of nonspecific adsorption to a pure DOPC bilayer, compared to avidin and streptavidin. In addition, the biotin-binding affinity of the antibiotin antibody was found to be of the same order of magnitude as that of avidin, streptavidin, and neutrAvidin. These findings provide important new insights into these biotin-bound protein complexes commonly used in several bioanalytical applications.