Differential scanning calorimetry study of the hydrophobic hydration of the elastin-based polypentapeptide, poly(VPGVG), from deficiency to excess ofwater

The polypentapeptide of elastin, poly(VPGVG), has become an interesting mod el polypeptide in understanding the mechanism of protein folding and assemb ly. Due to its simple amino acid composition and the predominance of apolar side chains, this polymer shows strong hydrophobic-hydration phenomena. Th is paper explores, by calorimetric methods, the nature and structure of the clathrate-like arrangements that take place, surrounding the apolar side c hains of the polymer. The performance of these methods, especially differen tial scanning calorimetry, has a well-gained reputation. In this work, the development of the clathrate-like structures around this model polymer has been followed from water deficiency to water-excess states. Two main conclu sions have been obtained from the data obtained. First, there is an upper l imit of about 170 water molecules per pentamer as the number of water molec ules required to form all the possible clathrate-like structures. Second, t hese structures exist as a inhomogeneous population with energies spreading in a significantly broad range, which is likely related to differences in geometrical parameters (bond lengths and angles) of the clathrate structure . (C) 2000 John Wiley & Sons, Inc.