The preparation and properties of alpha and beta pili from variants of Neisseria gonorrhoeae P9.

The alpha and beta type pili produced by variants of Neisseria gonorrhoeae P9 were isolated and characterized. The two types of pili showed clear differences in morphology, buoyant density (alpha, 1.292 g ml-1; beta, 1.282 g ml-1) and isoelectric point (alpha, pI 5.2; beta, pI 4.3). Amino acid analysis of alpha and beta pili showed that their overall composition was similar with the exception that beta pili had a higher content of glutamate and alanine residues. A high degree of structural homology was seen in two-dimensional peptide maps of tryptic hydrolysates of alpha and beta pili. The molecular differences between alpha and beta pili were reflected in their antigenic activity and in their ability to attach to human cells. The binding of alpha pili to buccal epithelial cells was pH dependent with a maximum binding of 49% at pH 6.5, whereas the attachment of beta pili showed no pH optimum. The binding of pili to erythrocytes differed from binding to buccal epithelial cells in that attachment of both pili was identical with no pH optimum. Data from attachment of pili to human cells suggest that erythrocytes lack receptors for binding gonococcal pili.