Structural changes in proteins resulting from homomolecular exchange at solid surfaces

The overall protein adsorption process comprises various steps or stages: transport of the protein from the bulk solution into the interfacial region, attachment of the protein at the sorbent surface and relaxation of the protein on the surface, detachment from the surface, and transport back into the solution.(1&2) Fig. 1 schematically shows the dynamics of the protein molecules moving from the solution to the surface and back: They continuously exchange between the adsorbed and the dissolved states. During relaxation, the protein-surface interactions are optimized, usually by some degree of spreading (unfolding) of the adsorbed protein molecules. The conformational changes involved in this step affect the biological functioning of the adsorbed molecules. For instance, the perturbation provoked by the sorbent surface largely modifies the activity of some enzymes(3) and antibodies(4) in the adsorbed state. Thus the occurrence of an interface and its consequences for the biological activity of proteins are of significant importance in biomedicine, food processing, environmental science, biotechnological applications, and analytical procedures. Depending on the extent of spreading the protein molecules undergo during relaxation, they may detach more or less readily from the sorbent surface. If detached, the question arises whether or not the protein molecules readopt their native conformation in solution