Thermal stability of the hydrogen-bonded water network in the hydration shell of isletamyloid polypeptide

Abstract

The effect of temperature on the connectivity of hydrogen bonds in the hydration shells ofthe islet amyloid polypeptides (IAPPs) is studied by means of computer simulations. Thehydrogen-bonded network of hydration water homogeneously envelopes a peptide at lowtemperature and breaks into an ensemble of small clusters upon heating. This thermalbreak occurs via a percolation transition, which is not found to be sensitive to the chemicalmodifications of IAPP (IAPP with and without a disulfide bridge, human and rat IAPP).The radius of gyration of IAPP starts to increase when the hydration water network breaksupon heating. The fluctuations of the number of intra-peptide hydrogen bonds shownegative correlation with the fraction of molecules in the largest cluster of hydrationwater. The thermal stability of the network of hydration water is enhanced uponincreasing number of intra-peptide hydrogen bonds, which makes the peptidesurface more hydrophobic. The thermal stabilities of the hydrogen-bonded waternetworks in the hydration shells of IAPPs and of several other biomolecules arefound to be rather similar: the network breaks between 300 and 330 K, i.e., in thetemperature interval where the biological activity of living organisms is maximal.