From Weak Interactions to Strong Affinity: Deciphering the Streptavidin-Biotin Interaction through NMR and ComputationalAnalysis
Understanding weak interactions in protein-ligand complexes is essential for advancing drug design. Here, we combine experimental and quantum mechanical approaches to study the streptavidin-biotin complex, one of the strongest known protein-ligand binders. Using a monomeric streptavidin mutant, we analyze 1H NMR chemical shift perturbations (CSPs) of biotin upon binding, identifying unprecedented upfield shifts of up to -3.2 ppm. Quantum chemical calculations attribute these shifts primarily to aromatic ring currents, with additional contributions from charge transfer effects linked to weak interactions. The agreement between experimental and computed chemical shifts validated the X-ray structure as a reliable basis for detailed computational analyses. Energy decomposition analysis reveals that electrostatics dominate the biotin-streptavidin interaction, complemented by significant orbital and dispersion contributions. Notably, weak non-covalent interactions--such as CH{middle dot} {middle dot} {middle dot} S, CH{middle dot} {middle dot} {middle dot}{pi} , and CH{middle dot} {middle dot} {middle dot} HC contacts--driven by London dispersion forces, contribute [~]44% to the complexs stability.