An Infrared Spectroscopic Study of the Conformational Transition of Elastin-Like Polypeptides

The infrared spectroscopy of elastin-like polypeptides and the relation to the inverse thermal transition are discussed. To correlate the spectroscopic observations with structure a density function theory model was created that captures the essential hydrogen bonding and packing of the β-spiral structure proposed for elastin and elastin-like polypeptides. The infrared spectrum was calculated using periodic boundary conditions and a method for estimating the difference dipole moment permits both frequencies and intensities to be obtained for the modeling of spectra. The two observed amide I bands at 1615 cm−1 and 1656 cm−1 are shown to arise from the β-spiral structure. The increase in intensity of these bands with increasing salt concentration and temperature is assigned to the closer association of strands of the β-spiral. The sharp inverse temperature transition is observed within 1°C and involves a change in secondary structure that involves formation of interstrand β-sheets for ∼25% of the amino acids. This conclusion is consistent with available data and simulations that have been reported to date.