W0086

Neutron Crystallography of Membrane Proteins. Peter Timmins, Eva Pebay-Peyroula, Simon Penel, Large Scale Structures Group, Institut Laue-Langevin, 38042 Grenoble Cedex 9, France

Neutron crystallography has been used to locate the detergent in three different crystal forms of porins from E. Coli and Rhodobacter Capsulatus. In X-ray diffraction experiments detergent and water are essentially indistinguishable and only a few well-ordered detergent molecules have been located. The relative contrasts for neutrons of any of the components in the crystals can be enhanced by soaking crystals in mixtures of H₂O and D₂O. The linearity of the complex structure factor as a function of contrast allows phase information to be derived as well as efficient scaling of data containing different amounts of D₂O. Contrast may also be varied by substituting components of a macromolecular complex with their perdeuterated analogues. The organisation of the detergent in the different porin crystals is radically different. In the Rhodobacter Capsulatus porin the crystals appear to be formed by simple condensation of the mixed protein/detergent micelle from solution. In the E.coli tetragonal form the same mixed micelle appears to be the building block of the crystal but detergent-detergent interactions are essential in its formation. Finally the trigonal form of the E. Coli protein requires a rearrangement of the detergent compared with the solution structure. In all cases the detergent binding is determined by a band of hydrophobic surface residues.

References

Pebay-Peyroula, E., Garavito, R.M., Rosenbusch, J.P., Zulauf, M. and Timmins, P.A. (1995) Detergent structure in tetragonal crystals of Ompf porin. Structure 3, 1051 - 1059.

Timmins, P.A., Pebay-Peyroula, E. & Welte, W. (1994) Detergent Organisation in Solution and in Crystals of Membrane Proteins. Biophys. Chem. 53 (1-2), 27 - 36.

Penel, S., Pebay-Peyroula, E. Rosenbusch, J., Rummel, G., Schirmer, T. and Timmins, P. (1998) Detergent binding in trigonal crystals of Ompf porin from E.Coli Biochimie (submitted)