Dehydration-induced Initial Conformational Change of Hydrated Proteins Detected by the Changes in Vibrational Circular Dichroism Activity

Conformational changes of hydrated proteins induced by gradual dehydration were monitored by vibrational circular dichroism (VCD) spectroscopy. In myoglobin and casein, representative alpha-helix-rich and random-coil proteins, respectively, an increase in left-handed optical activity in the amide I band was detected at the initial stage of dehydration, followed by an increase in opposite right-handed activity in both the amide I and II bands with further dehydration. Because the second step was observed with an increase in the turbidity of the proteins, it can be attributed to their aggregation. In contrast, because the increase in left-handed optical activity is induced by the conformational change of the proteins and is followed by the aggregation, it may derive from the increase in the regularity of the local structure in individual myoglobin or casein that triggers the aggregation.