Fragmentation of Escherichia coli type 1 fimbriae exposes cryptic D-mannose-binding sites

Abstract

Cells of the gram-negative bacterium Escherichia coli are able to attach to various host cells by means of a mannose-specific adhesin associated with type 1 fimbriae. Here we show that fragmentation of type 1 fimbriae by freezing and thawing results in increased mannose-binding activity as demonstrated by increased hemagglutination, increased stimulation of human lymphocyte proliferation, and increased binding of the mannose-containing enzyme horseradish peroxidase. Increased activity in all three assays was mannose sensitive and was not exhibited by FimH-mutant type 1 fimbriae lacking the adhesin. Scatchard analysis of the data from peroxidase binding assays showed that unfrozen and frozen fimbriae contain binding sites displaying two classes of affinity. Frozen and thawed fimbriae expressed an increase in the number of highaffinity binding sites. These results show that fragmentation of the fimbrial structure exposes cryptic mannosebinding activity associated with type 1 fimbriae, presumably that of internally located adhesin molecules. Our data support earlier observations that adhesin moieties of type 1 fimbriae are located both at the tips and at intervals along the length of the fimbriae. In addition, our data suggest that only the adhesin moieties that are located at the fimbrial tips are functional in binding mannose. Adhesins located along the length of the fimbriae have their mannose-binding activity buried within the fimbrial structure and hence are not functional. We propose an updated model for the structure of type 1 fimbriae that is in agreement with the above observations. Several members of the family Enterobactericeae, including most strains of Escherichia coli, express on their surfaces numerous proteinaceous filaments called fimbriae. The fimbriae expressed by E. coli can be of one or more types based on the specific mode of recognition or interaction mediated by these organelles in promoting adherence of the bacteria to various host cell surfaces (10,12,13,19). In this respect, among the more common fimbriae expressed by E. coli are type 1 fimbriae, which are known to facilitate attachment of the bacteria to mannose-containing receptors exposed on a variety of host cells (4,17,18,22). The mannose-binding activity associated with type 1 fimbriae is commonly demonstrated by specific adhesion assays, including mannose-sensitive agglutination of guinea pig erythrocytes (21). Facilitated adherence of the bacteria to mannose-containing glycoproteins on host cells is believed to be an important prerequisite for successful invasion and colonization in the pathogenesis of several E. coli and other enterobacterial infections (2, 3, 7). Recently, we have found that type 1 fimbriae can also stimulate human lymphocyte proliferation, which is mannose sensitive (20).The structure of type 1 fimbriae was initially described by Brinton as being entirely composed of 17-kDa protein subunits, now It has also been demonstrated that FimH by itself is the mannose-specific adhesin of type 1 fimbriae (11).Although ...

The Pix pilus adhesin of the uropathogenic Escherichia coli strain X2194 (O2 : K− : H6) is related to Pap pili but exhibits a truncated regulatory region

“…In addition, in the sfp operon, homologues of papI and papB could not be detected (Brunder et al, 2001). As the pix operon apparently does not contain genes encoding a tip-associated fibrillum, these data might indicate that the actual adhesin might not be located at the tip but instead could be periodically intercalated in the pilus rod (Ponniah et al, 1991).…”

Snapshots of usher-mediated protein secretion and ordered pilus assembly

“…Thus, the oligomeric complex in the FimDCGH sample may consist primarily of a rod-like structure. It has been suggested previously that occasionally FimH can be intercalated within the type 1 pilus rod (30,34,35); the relative quantities of FimG and FimH in the FimDCGH assembly intermediate (Fig. 2 A, lane 2) suggest that there may be multiple FimH subunits in the multimer that is formed.…”

“…One hypothesized explanation for this phenomenon was pilus retraction, and another was physical impedance of outward pilus growth by the host cell (3). It has been suggested previously that FimH intercalation would result in relatively weak points in the type 1 pili, which are thought to be prone to breakage (35). Such breakage could also account, in part, for the shortening of pili that has been seen during the early stages of infection (3).…”

“…After pilus breakage, newly exposed FimH adhesins (ref. 35 and unpublished data) could promote bacterial attachment and invasion of underlying epithelial cells.…”

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

“…However, for this to be true, FimH presented at the fimbrial tip as well as FimH intercalated along the shaft would both have to be able to mediate adhesion. Much previous work has indicated that only FimH present at the tips of fimbriae is functional in mediating adhesion (35,(45)(46)(47)(48). For example, type 1 fimbriae have been observed to bind to erythrocyte membranes as well as the uroepithelium by the tips of the fimbriae (46,49).…”