Volumetric properties of human islet amyloidpolypeptide in liquid water

Abstract

The volumetric properties of human islet amyloid polypeptide (hIAPP) in water were studied in a wide temperature range by computer simulations. The intrinsic density ρ_p and the intrinsic thermal expansion coefficient α_p of hIAPP were evaluated by taking into account the difference between the volumetric properties of hydration and bulk water. The density of hydration water ρ_h was found to decrease almost linearly with temperature upon heating and its thermal expansion coefficient was found to be notably higher than that of bulk water. The peptide surface exposed to water is more hydrophobic and its ρ_h is smaller in conformation with a larger number of intrapeptide hydrogen bonds. The two hIAPP peptides studied (with and without disulfide bridge) show negative α_p, which is close to zero at 250 K and decreases to ≈−1.5 × 10⁻³ K⁻¹ upon heating to 450 K. The analysis of various structural properties of peptides shows a correlation between the intrinsic peptide volumes and the number of intrapeptide hydrogen bonds. The obtained negative values of α_p can be attributed to the shrinkage of the inner voids of the peptides upon heating.