Analyse of two porin crystals
(Ph. D. 1997)
Penel S., Pebay-Peyroula E., Timmins P.,
Welte W., Hovers, J.,
Rosenbusch J., Rummel G., Schirmer T.
Summary
Despite the high importance of membrane proteins in biological function, the number of such structures which
have been solved is very small, because of the difficulty in producing good quality crystals. The detergent in
which the protein has to be partially solubilised plays a crucial role particularly as it protects the hydrophobic
transmembrane surface of the protein during the extraction of the protein from the membrane.
A knowledge of the structure of detergents in protein crystals can yield a better understanding of the
interactions between protein and membrane, the detergent playing the same role as the membrane, and of the
effect of the detergent in the crystallization process. Using low resolution neutron crystallography (DB21
diffractometer, Institut Laue-Langevin, Grenoble France) combined with contrast variation, a well adapted
technique for this study of disordered structures, the structure of detergents in two membrane protein crystals, an
E. coli porin (P321 crystal) and a Rhodobacter capsulatus porin (R3 crystal), have been solved.
In both studies, the detergent forms micellar structures around the transmembrane surface of the protein, the
micellar borders are limited by specific interactions with aromatic amino acids forming two rings playing a role
in stabilizing the protein in the membrane. Theses studies show that the dimensions of the hydrophobic and
hydrophilic moieties of the detergent is a determinant factor in order to favour protein-protein contacts during the
nucleation and the crystal growth.
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