Porins from the outer membrane of Gram-negative bacteria are generally non-selective, transmembrane channels. The pore structure is formed almost entirely of a beta-barrel (shown above); the monomeric protein is matured into a trimeric species which is integrated into the outer membrane. Omp F porin was first crystallized by R. M. Garavito in 1979.
As part of an effort to understand how integral membrane proteins interact with amphipathic components like lipids and detergents and to improve crystallization methods, OmpF porin crystals were studied using neutron diffraction and "density-matching". Here, the torus of detergent around a trimer of OmpF porin is clearly seen.
References of Interest
Cowan, S. W., Garavito, R. M., Jenkins, J., Pauptit, R. A., Karlsson, R., G. Rummel, Pai, E., Rizkallah, P. J., Rosenbusch, J. P., Jansonius, J. N., Schirmer, T. (1995) "The structure of the outer membrane protein porin in a tetragonal crystal form." Structure 3, 1041-1050.
Pebay-Peyuola, E., Garavito, R.M., Rosenbusch, J.P., Zulauf, M., and Timmins, P.A. (1995) "Detergent structure in tetragonal crystals of porin from the outer membrtane of E. coli." Structure 3, 1051-1059.