Interaction of two variable proteins (PilE and PilC) required for pilus‐mediated adherence of Neisseria gonorrhoeae to human epithelial cells

Abstract

Pili confer the initial ability of Neisseria gonorrhoeae to bind to epithelial cells. Pilin (PilE), the major pilus subunit, and a minor protein termed PilC, reportedly essential for pilus biogenesis, undergo intra-strain phase and structural variation. We demonstrate here that at least two different adherence properties are associated with the gonococcal pili: one is specific for erythrocytes, which is virtually unaffected by PilE variation, and another is specific for epithelial cells, and is modulated in response to the variation of PilE. Based on this finding, mutants of a recA- strain were selected that had lost the ability to bind to human cornea epithelial cells (A-) but retained the ability to form pili (P+) and to agglutinate human erythrocytes (H+). The adherence-negative mutants failed to produce detectable levels of PilC1 or PilC2 proteins, representing piIC phase variants generated in the absence of RecA. The A- pilC phase variants were indistinguishable from their A+ parents and spontaneous A+ revertants with regard to the amount of PilE produced and its electrophoretic mobility, the degrees of piliation and haemagglutination, and the pilE nucleotide sequence. These data demonstrate a central role for PilC in pilus-mediated adherence of N. gonorrhoeae to human epithelial cells and further indicate that neither PilC1 nor PilC2 is obligatory for the assembly of gonococcal pili.

A Novel Interaction Between Type IV Pili ofNeisseria gonorrhoeaeand the Human Complement Regulator C4b-Binding Protein

“…We found that four pili variants containing different PilE sequences (38) bound C4BP with similar apparent affinities (not shown). PilC is a 110-kDa pilus biogenesis protein that seems to be involved in the interaction between pili and MCP, because it was possible to select or genetically construct adherence negative mutants that expressed pili without detectable amounts of PilC (39,40). The results of an overlay assay suggested that C4BP interacts with the PilC subunit of pili.…”

Variation of gonococcal lipooligosaccharide structure is due to alterations in poly-G tracts in lgt genes encoding glycosyl transferases.

“…A 110-kD protein, pilC, present in small amounts in pill, is responsible for adherence to epithelial cells. The expression of this protein is subject to high frequency variation by a frame-shift mechanism due to a stretch of G residues early in the coding frame (10,11). The opacity proteins (opa) are also important adhesins.…”

“…This suggested that the high frequency antigenic variation of GC LOS could be due to slipped strand mispairing during replication, causing premature termination of translation. This form of variation has been seen in the case of the pilC protein (10), a G.C pilus accessory protein imparting adhesiveness to epithelial cells (11). The glycosyl transferases that might be subject to this form of variation are IgtA, the GlcNAc transfer~tse; lgtD, the GalNAc transferase; and IgtC, the Gal Xransferase responsible for the addition of o~Gall-4f3Gal.…”

Neisseria gonorrhoeae PilV, a type IV pilus-associated protein essential to human epithelial cell adherence

“…However, several studies have suggested a role for the pilin subunit PilE in receptor recognition. These include numerous findings showing that different antigenic variant forms of PilE influence epithelial cell adherence and tissue tropism (12,(14)(15)(16). However, the structural and functional attributes of PilE accounting for these observations remain unknown.…”

“…The conclusion that PilC is a neisserial Tfp-associated adhesin is based primarily on the findings that (i) purified recombinant PilC imparts human epithelial cell binding activity on latex beads to which it has been coupled and blocks binding of piliated organisms to human epithelial cells (7) and (ii) piliated mutants lacking PilC fail to adhere (12,13). However, several studies have suggested a role for the pilin subunit PilE in receptor recognition.…”