PORIN POLYPEPTIDE CONTRIBUTES TO SURFACE-CHARGE OF GONOCOCCI

Each strain of Neisseria gonorrhoeae elaborates a single porin polypep tide, with the porins expressed by different strains comprising two ge neral classes, Por1A and Por1B. In the outer membrane, each porin mole cule folds into 16 membrane-spanning beta-strands joined by top- and b ottom-loop domains. Por1A and Por1B have similar membrane-spanning reg ions, but the eight surface-exposed top loops (I to VIII) differ in le ngth and sequence. To determine whether porins, and especially their t op loop domains, contribute to bacterial cell surface charge, strain M S11 gonococci that were identical except for expressing a recombinant Por1A, Por1B, or mosaic Por1A-1B polypeptide were compared by whole-ce ll electrophoresis. These porin variants displayed different electroph oretic mobilities that correlated with the net numbers of charged amin o acids within surface-exposed loops of their respective porin polypep tides. The susceptibilities of porin variants to polyanionic sulfated polymers correlated roughly with gonococcal surface charge; those pori n variants,vith diminished surface negativity showed increased sensiti vity to the polyanionic sulfated compounds. These observations indicat e that porin polypeptides in situ contribute to the surface charge of gonococci, and they suggest that the bacterium's interactions with lar ge sulfated compounds are thereby affected.