Infection and Immunity
The JS3 and FA638 strains of Neisseria gonorrhoeae bear a protein IA subclass of protein I (P.I). The purified P.Is of surface-labeled strains JS3 and FA638 were cleaved with the N-terminal degradation enzyme leucine amino peptidase (LAP), and the resultant fragments were separated in sodium dodecyl sulfate-polyacrylamide gels. Autoradiography demonstrated that the surface radiolabel was absent in a LAP-generated P.I peptide that was about 1,900 daltons lower in apparent molecular mass than the native P.I in both strains. Moreover, the 4G5 monoclonal epitope, known to be located on the surface of the organism, was also absent in the LAP-generated P.I peptide that was about 1,900 daltons less in apparent molecular mass than the original P.I of strain FA638. These data strongly suggest that the N terminus of the P.IA subclass is exposed on the surface of the bacterium and that this region represents about 5%, or 15 to 20 amino acids, of the total protein.