The Distinct Binding Specificities Exhibited by Enterobacterial Type 1 Fimbriae Are Determined by Their Fimbrial Shafts

Abstract

Type 1 fimbriae of enterobacteria are heteropolymeric organelles of adhesion composed of FimH, a mannose-binding lectin, and a shaft composed primarily of FimA. We compared the binding activities of recombinant clones expressing type 1 fimbriae from Escherichia coli, Klebsiella pneumoniae, and Salmonella typhimurium for gut and uroepithelial cells and for various soluble mannosylated proteins. Each fimbria was characterized by its capacity to bind particular epithelial cells and to aggregate mannoproteins. However, when each respective FimH subunit was cloned and expressed in the absence of its shaft as a fusion protein with MalE, each FimH bound a wide range of mannose-containing compounds. In addition, we found that expression of FimH on a heterologous fimbrial shaft, e.g. K. pneumoniae FimH on the E. coli fimbrial shaft or vice versa, altered the binding specificity of FimH such that it closely resembled that of the native heterologous type 1 fimbriae. Furthermore, attachment to and invasion of bladder epithelial cells, which were mediated much better by native E. coli type 1 fimbriae compared with native K. pneumoniae type 1 fimbriae, were found to be dependent on the background of the fimbrial shaft (E. coli versus K. pneumoniae) rather than the background of the FimH expressed. Thus, the distinct binding specificities of different enterobacterial type 1 fimbriae cannot be ascribed solely to the primary structure of their respective FimH subunits, but are also modulated by the fimbrial shaft on which each FimH subunit is presented, possibly through conformational constraints imposed on FimH by the fimbrial shaft. The capacity of type 1 fimbrial shafts to modulate the tissue tropism of different enterobacterial species represents a novel function for these highly organized structures.

Escherichia coli Common Pilus (ECP) Targets Arabinosyl Residues in Plant Cell Walls to Mediate Adhesion to Fresh Produce Plants

“…EcpD can be secreted and polymerized/oligomerized in the absence of EcpA (18) as an "afimbrial" adhesin, although the processes may not be as efficient as in the presence of EcpA. Moreover, as with type 1 fimbriae, EcpA itself could play a role in the specificity (68). Our data show that the EcpA fimbrial structure is required for presentation of EcpD to target cell wall arabinans during interactions with plant hosts.…”

Molecular Variations in Klebsiella pneumoniae and Escherichia coli FimH Affect Function and Pathogenesis in the Urinary Tract

“…Two differences in K. pneumoniae TOP52 primary sequence exist in residues adjacent to these mannose-binding residues at positions 132 and 141. Data from the threaded model suggest that at least two hydrogen bonds are lost in FimH 52 with the combined differences in residues 132 and 141, which may have a destabilizing effect on interactions at the mannose site around the Asp140 and Gln133 mannose-binding resi- (16,38). These effects do not account for the binding specificity differences observed for FimH 52 .…”

Biofilms: Microbial Cities of Scientific Significance

“…Type I fimbria are filamentous proteinaceous adhesins that are found in pathogenic as well as commensal (existence of symbiotic relationship between the organisms) strains of E. coli and vary between 100-500 fimbria on the surface of the bacteria. Studies have shown their association with the virulence of the pathogen [57,58]. In addition, well documented scientific evidences have been provided by researchers to substantiate the role of fimbria in the formation of secreted IgA mediated biofilm formation within the gut [59].…”