Resolution of basic gonococcal outer membrane proteins by nonequilibrium pH gradient electrophoresis.
Outer membrane proteins from opaque and transparent colonial variants of strain F62 of Neisseria gonorrhoeae were analyzed by two-dimensional electrophoresis with isoelectric focusing in the first dimension and sodium dodecyl sulphate-polyacrylamide gel electrophoresis in the second. Most of the higher-molecular-weight proteins focused sharply in the acidic region of the gel. In contrast, the principal outer membrane protein, a 31,000-molecular-weight protein, and the opacity-associated proteins remained near the origin (at the basic end of the gel) without focusing. However, when the samples were loaded on the acidic end of an isoelectric focusing gel and subjected to nonequilibrium pH gradient electrophoresis, these proteins behaved as basic proteins. In addition, three distinct opacity-associated heat-modifiable proteins could be identified. No other differences in the protein composition of outer membranes from opaque and transparent variants were apparent. Amino acid analysis of the principal outer membrane protein indicated that its net positive charge may result from partial amidation of its acidic residues. The unexpected observation that the major surface proteins of the gonococcus are basic may have implications for intragonococcal adhesion and for gonococcal interactions with mammalian cells.