PROTEIN ADSORPTION-KINETICS DRASTICALLY ALTERED BY REPOSITIONING A SINGLE CHARGE

A sterically conservative, neutralizing mutation (glutamic acid to glutamine) in either of two different positions (15 or 48) of the soluble core tryptic fragment of cytochrome b5 results in two proteins with vastly different adsorption properties. The kinetics of adsorption were measured under well-defined hydrodynamic conditions on a variety of different surfaces, of controlled electrostatic potential, prepared by modifying planar optical waveguides. Repeated measurement of the guided mode spectrum in the presence of protein solution allowed the temporal evolution of the number of adsorbed molecules to be determined. A highly positively charged surface acted as a perfect sink, i.e., adsorption was only limited by transport, adsorption to a highly negatively charged surface was fully reversible, and adsorption to a neutral phospholipid bilayer was very slow and practically irreversible. The macroscopic adsorption behavior can in large part be interpreted in terms of molecular-scale interactions between the protein and the adsorbent surface.