X-RAY DIFFUSE SCATTERING FROM A LYSOZYME CRYSTAL ANALYSED WITH A RIGID-BODY MODEL OF DISPLACEMENTS. J. Perez, Ph. Faure and J.-P. Benoit, LURE, CNRS-CEA-MENESR, Bat. 209D, Universite Paris-Sud, F-91405 Orsay Cedex, France
X-ray cloudy diffuse scattering from a tetragonal crystal of lysozyme has been collected at room temperature on the wiggler W32 station of LURE synchrotron and interpreted with a simple model of rigid-body displacements. Cloudy diffuse scattering is the part of the scattered intensity which arises from atomic displacements not correlated from cell to cell, and is therefore the signature of intramolecular or molecular correlations.
It is shown here that most of the pattern can be considered as due to independent rigid-body translations and rotations of the protein molecules within the crystal. The normal-mode analysis performed on a single molecule of lysozyme, which accounts only for the intramolecular correlations [Faure et al., 1994], results in a too smooth pattern, underlying the existence of displacements correlated at the molecular scale. By further performing an analysis of the temperature factors of the individual atoms, derived from the crystallographic refinement, it is possible to estimate the mean-square displacement due to the molecular rigid-body motion. The respective values are 0.1Å2for rotations and 0.1Å2 for translations.
The present diffuse scattering analysis confirms and completes the TLS hypothesis proposed in 1979 by Artymiuk et al., in the sense that it allows to differentiate between a rigid-body rotation movement and a breething movement of the proteins and to estimate the part of the total disorder due to rigid-body tranlations of the whole molecules.
References:
Artymiuk, P.J., Blake, C.C.F., Grace, D.E.P., Oatley, S.J., Phillips, D.C., Sternberg, M.J.E. (1979), Nature, 280, 563-568.
Faure, Ph., Micu, A., Perahia, D., Doucet, J., Smith, J., Benoit, J.P. (1994), Nature:Structural Biology, 1, 124-128.