Electron microscopy of the major outer membrane protein of Campylobacter jejuni

The surfaces of the disrupted-cell surfaces of the Campylobacter jejuni strains FUM158432 and M1 were examined using the negative-staining technique and electron microscopy. The surfaces of the whole cells and the outer membranes were covered with small dark dots which, in some areas, were arranged in hexagonal patterns. The hexagonal arrangement was more clearly seen in extracted outer membrane. The size of each structure was measured based on a center-to-center distance with the adjacent structure, and was determined to be 9.9+/-0.9 nm. A profile of the proteins in the outer membrane by SDS-PAGE, performed in 0.1% SDS and at 100 C, showed 42 kDa proteins to comprise the major outer membrane protein of this bacterium. Digestion of the outer membrane materials with proteinase reduced this protein band in the SDS-PAGE, and the amount of dark dots on the electron micrograph indicated the structure to be the major outer membrane protein (porin) of this bacterium. The power spectrogram of a computer-assisted Fourier transformation of the hexagonally arranged porin proteins suggests that the porin has a trimeric structure rather than a monomeric one.