Most of the studies to date which examine how bacteria attach to and become internalized by host cells have been based on the hypothesis of a unidirectional attachment. In other words, the bacteria (cell A) express a receptor protein which binds to a ligand on the host cell (cell B). However, most eukaryotic cells bind to each other bidirectionally which can be categorized into three general binding mechanisms; i.e. homophilic, heterophilic, or extracellular linker adherence. Few studies have directly examined if pathogenic bacteria engage in these other types of bidirectional binding mechanisms to their host cells. In this proposal, we will give preliminary evidence that would support the hypothesis that the gonococcus employs bidirectional adherence mechanisms not only between two gonococci but also between gonococci and human host cells. Heterophilic bidirectional binding is when receptor-like molecules on one cell bind to ligand-like structures on adjacent cells and vice versa. We have recently completed studies which would suggest that the intercellular connections between gonococci displaying the opaque colony phenotype is such a heterophilic adherence. The receptor in this case is the opacity related proteins II (pII) expressed by these gonococci. The ligand to which these pIIs bind is the terminal Gal(beta1-4)GlcNAc structure found on the gonococcal lipooligosaccharides (LOS). These terminal and preterminal saccharide residues contained in the oligosaccharide component of the LOS of N. gonorrhoeae have been found to be identical immunochemically to human asialoparagloboside residues. In examining whether gonococcal pIIs would bind to these human carbohydrates, we establish that pII could adhered to these human glycolipids equally well. This Gal(beta1-4)GlcNAc structure is found on a variety of human cells and glycoproteins. The glycoproteins containing this moiety in a terminal position are commonly known as asialoglycoproteins because they are usually derived by the loss of a terminal sialic acid residue which is linked to the terminal galactose via a 2-6 linkage. The loss of this terminal sialic acid is thought to be a sign of """"""""aged"""""""" glycoproteins. Known asialoglycoprotein receptors are found on a variety of human cells and these receptors are involved in the selective removal by intracellular uptake of cells and proteins expressing these asialoparaglobosides. The purpose of this proposal is to specifically examine if gonococci engage in bidirectional adherence with human cells using either the heterophilic or extracellular linker type mechanisms. We are especially interested the role these mechanisms may play in invasion of the upper genital tract, in particular Fallopian tube and endometrial cells. Thus, the close cellular adhesions observed between gonococci of the opaque colony phenotype, generated by pII proteins of one organism adhering to the LOS of the opposite organism, are possibly quite similar to the close cellular adhesions seen between gonococci and human cells with the exception that the bacterial pII proteins are replaced by mammalian asialoglycoprotein receptors and the bacterial LOS is replaced by asialoparaglobosides. It is our belief that this mechanism is involved in the uptake of the gonococcus by human cells.
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