The Campylobacter jejuni porin trimers pack into different lattice types when reconstituted in the presence of lipid

Purified major outer membrane protein of Campylobacter jejuni exhibited different classes of molecules by SDS/PAGE and immunoblotting. A high-molecular-mass product (120-140 kDa) was observed under mild conditions of solubilization, a folded monomeric form of 35 kDa was seen when treated at high SDS concentrations and finally, a single band around 45 kDa occurred when the sample was heated to 96 degrees C [Bolla, J. M., Loret, E., Zalewski, M. & Pages, J. M. (1995) J. Bacteriol. 177, 4266-4271]. The high-molecular-mass product was reconstituted into two-dimensional crystals in the presence of phospholipids and Mg2+. The C. jejuni porin required different conditions for successful reconstitution into two-dimensional crystals than the Escherichia coli porin OmpF. Electron microscopy and digital image processing of negatively stained specimens revealed a rectangular lattice with a unit cells size of a = 8.9 nm, b = 14.9 nm, an oblique lattice with a = 8.9 nm, b = 30.1 nm, gamma = 98 degrees, and a trigonal lattice with a = b = 9.6 nm. Projection maps were calculated to a resolution of 2 nm, and exhibited a trimeric protein with three stain-filled indentations.