Gonococcal protein III. Purification and chemical characterization of the protein,and the DNA sequence of the structural gene

We have purified protein III (PIII) from several strains of gonococcus by extractions with Zwittergent 3,14 followed by cation exchange chromatography and gel filtration. The pI of 8.6 determined by isoelectric focusing was in keeping with the high content of basic amino acids found. PIII from two strains had identical N-terminal sequence. In contrast to PIII in vivo, purified PIII was highly susceptible to proteolysis. Rabit antibodies raised with purified antigen reacted with PIII of all strains tested as well as meningococcal protein 4. Furthermore, intact gonococci or meningococci could absorb 80% of antibodies raised by immunization with the purified PIII. The structural gene of PIII was cloned and the DNA sequenced. The predicted primary structure is strongly homologous to the OmpA proteins of Enterobacteria.