VARIATION WITHIN SEROVARS OF NEISSERIA-GONORRHOEAE DETECTED BY STRUCTURAL-ANALYSIS OF OUTER-MEMBRANE PROTEIN PIB AND BY PULSED-FIELD GEL-ELECTROPHORESIS

Outer-membrane protein PI is the antigen responsible for serovar speci ficity of Neisseria gonorrhoeae and is a potential vaccine target. In order to investigate possible hidden variation within a serovar, the s equence of the por genes encoding protein PIE have been obtained from a series of strains, including isolates known to be epidemiologically linked. The inferred amino acid sequences of the PIE molecules of isol ates from known sexual contacts were identical, but non-related isolat es showed significant heterogeneity in PIE sequence. These differences were not confined to the two variable regions (Var1 and Var2) which h ave previously been identified, but were largely, although not exclusi vely, located in regions predicted to form one of eight surface-expose d loops. The isolates were subjected to pulsed-field gel electrophores is of restriction digests of chromosomal DNA, which also demonstrated identity between linked strains but revealed diversity within a serova r. The deduced amino acid sequences of PIE were also used to synthesiz e peptides for epitope-mapping experiments. These revealed that some m Abs, used to define serovar specificity, recognized linear epitopes lo cated in loops 5 and 6, while others appeared to recognize conformatio nal epitopes elsewhere in the molecule. The occurrence of the sequence differences within a serovar, which are not detected by the serotypin g reagents, reveals that PIE represents a potential source of informat ion which should permit considerably more detailed epidemiological stu dies than are currently possible and focuses attention on more conserv ed regions of the protein as potential targets for vaccination.