Functional expression of heterologous fimbrial subunits mediated by the F41, K88, and CS31A determinants of Escherichia coli

Abstract

F41, K88, and CS31A are fimbrial adhesins associated with enterotoxigenic Escherichia coli. These adhesins are distinct from one another in the composition of their structural subunits and the adherence characteristics associated with their expression. Despite these differences, extensive homology exists between the genetic determinants mediating the expression of these adhesins, extending throughout the region of each determinant encoding the accessory proteins involved in adhesin biogenesis. This suggests that the regulatory and assembly systems mediating expression of these adhesins may be functionally interchangeable. In the present study we demonstrated that the accessory systems of the F41, K88, and CS31A determinants are able to mediate the functional expression of heterologous fimbrial subunit proteins. Plasmid constructs containing the isolated fimbrial subunit gene of the F41 or CS31A determinant were prepared and introduced into E. coli harboring the F41, K88, and CS31A accessory genes contained on compatible plasmid vectors. The ability of each of the three accessory systems to mediate stable expression of the F41 or CS31A fimbrial subunit peptide was demonstrated by Western blot (immunoblot) analysis. Functional expression of the F41 or CS31A subunit on the bacterial cell surface was demonstrated by the ability of these proteins to confer mannose-resistant hemagglutination of human erythrocytes or in vitro adherence to epithelial cells, respectively. The accessory system of an unrelated adhesin determinant, F1845, did not mediate functional expression of F41 adherence. Taken together, these data indicate that the genetic determinants mediating expression of the F41, K88, and CS31A adhesins are members of a closely related family and suggest that a mechanism exists in the family for the more rapid divergence of genes encoding antigenic and adhesive determinants.