A Monte Carlo analysis of the elastic incoherent neutron scattering data in hydrated azurin Original Research Article

We measured the incoherent neutron scattering elastic intensity of hydrated copper azurin at different temperatures in a wide momentum transfer q range. The results show a well-defined non-Gaussian q dependence above 180 K. To investigate the nature of the motions underlying this non-Gaussian dependence, we used a Monte Carlo method to interpret the elastic intensity as the superposition of individual non-dynamically equivalent Gaussian contributions. The calculated probability distribution functions corresponding to such a decomposition are analysed as a function of the temperature. The onset of large amplitude Gaussian motions is responsible for the mean square displacements behaviour, which show above 210 K a marked departure from the harmonic temperature dependence. In addition, such an approach allowed us to correlate the elastic intensity q dependence with the boson peak, a characteristic low-frequency anomaly of protein inelastic spectra.