Vibrational neutron spectroscopy of collagen and model polypeptides

Abstract

A pulsed source neutron spectrometer has been used to measure vibrational spectra (20-4000 cm-1) of dry and hydrated type I collagen fibers, and of two model polypeptides, polyproline II and (prolyl-prolyl-glycine)10, at temperatures of 30 and 120 K. the collagen spectra provide the first high resolution neutron views of the proton-dominated modes of a protein over a wide energy range from the low frequency phonon region to the rich spectrum of localized high frequency modes. Several bands show a level of fine structure approaching that of optical data. The principal features of the spectra are assigned. A difference spectrum is obtained for protein associated water, which displays an acoustic peak similar to pure ice and a librational band shifted to lower frequency by the influence of the protein. Hydrogen-weighted densities of states are extracted for collagen and the model polypeptides, and compared with published calculations. Proton mean-square displacements are calculated from Debye-Waller factors measured in parallel quasi-elastic neutron-scattering experiments. Combined with the collagen density of states function, these yield an effective mass of 14.5 a.m.u. for the low frequency harmonic oscillators, indicating that the extended atom approximation, which simplifies analyses of low frequency protein dynamics, is appropriate.

Collagen and component polypeptides: Low frequency and amide vibrations

“…5 shows the relative scales of the different contributions from which it can be seen that the proline contribution is still the dominant one at 600 cm À1 , (the doublet peaks would reach the top of the figure if the pDOS were weighted by the number of protons). This result is consistent with the main effect of deuteration of labile protons, reported in [29], which is a reduction in spectral intensity from 500 to 750 cm À1 .…”

“…The measured INS spectrum of dry PPG 10 [29] is shown in Fig. 3, panel d. The corresponding calculated spectrum is shown in Fig.…”

“…3 (panels a, b) and 4 (panels a, c) show, respectively, the measured and calculated INS spectra for PG-II and PP-II. The experimental data are taken from [40,29], respectively. Fig.…”

“…We exploit high frequency spectra to investigate the structure-dynamics relation and the accuracy of solid state, DFT methods in this context. In the case of collagen, the goal is to establish a spectral signature of the triple-helix [29]. By studying dry, homo-polymers and wet, hetero-polymers, a range of computational challenges are encountered, especially with respect to the low frequency dynamics of collagen.…”

Hydration water and peptide dynamics – two sides of a coin. A neutron scattering and adiabatic calorimetry study at low hydration and cryogenic temperatures

“…Nevertheless, many aspects regarding its particular structure near the surface and inside biological macromolecules as well as its link to biological function are still under discussion. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Proteins are known to have a ''limiting hydration'' necessary for function, and thus there must exist a link between hydration and protein functional properties.…”