Conformational changes in proteins at interfaces: from solution to the interface, and back

After adsorption, polymer molecules, including proteins, undergo conformational relaxation. It involves a certain degree of spreading of the polymer molecule over the sorbent surface. Adsorption kinetics experiments reveal that the characteristic time of spreading is much longer for globular proteins than for highly flexible polymers. Based on differential scanning calorimetry it is concluded that the degree of spreading of protein molecules decreases with increasing rate of covering the surface with the protein. It is furthermore inferred that the relaxation does not proceed gradually but rather in steps. According to circular dichroism spectra the relaxed protein molecules still contain a large fraction of ordered structure. As a rule, protein molecules that, by homomolecular exchange, are released from the surface re-adopt their original structure; however, an exception to this rule is reported.