Fimbrial adhesins: similarities and variations in structure and biogenesis

Abstract

Fimbriae are wiry (2 to 4 nm diam.) or rod-shaped (6 to 8 nm diam.), fibre-like structures on the surfaces of bacteria which mediate attachment to host cells. Much has been learned in recent years about the biogenesis, structure and regulation of expression of these adhesive organelles in Gram-negative bacteria. Analyses of the genetic determinants encoding the biogenesis of fimbriae has revealed that the adhesive interaction of fimbriae can be mediated by major subunits (CFA/I and CS1 fimbriae) or minor subunits (P, S, and type 1 fimbriae), with the adhesin being located either at the tip of the fimbria or along the length of the fimbrial shaft. Minor subunits can also act as adapters, anchors, initiators or elongators. Post-translational glycosylation of the type 4 pilins of Neisseria gonorrhoeae, Neisseria meningitidis and Pseudomonas aeruginosa has been demonstrated. The structures of the PapD chaperone of Escherichia coli and of N. gonorrhoeae type 4 fimbrin have been resolved at 2.0-2.6 A. Rod-shaped fimbriae should not be thought of as being rigid inflexible structures but rather as dynamic structures which can undergo transition from a helicoidal to a fibrillar conformation to provide a degree of elasticity and plasticity to the fimbriae so that they can resist shear forces, rather like a bungee cord. At least four mechanisms have been identified in the assembly of fimbriae from fimbrin subunits, namely the chaperone-usher pathway (e.g., P-fimbriae of uropathogenic E. coli), the general secretion assembly pathway (e.g., type 4 fimbriae or N-methylphenylalanine fimbriae of P. aeruginosa, the extracellular nucleation-precipitation pathway (e.g., curli of E. coli) and the CFA/I, CS1 and CS2 fimbrial pathway.

Animal EnterotoxigenicEscherichia coli

“…Thick helical fimbriae can be stretched under certain in vitro conditions (117) or by using force to unwind the helix (118), accompanied by conformational changes in fimbrial subunits. It has been suggested that fimbrial stretching occurs in vivo to adjust and coordinate the lengths of the few hundred fimbrial threads anchoring the colonizing bacteria that are submitted to the intestinal peristalsis and its resulting shear force (119). Fimbriae-mediated bacterial adhesion to a target cell is enhanced by shear force, as described with F41 fimbriae (120).…”

Stopping Bacterial Adhesion: A Novel Approach to Treating Infections

“…Flagellae, pili, fimbriae and outer membrane proteins may all be required for bacterial adhesion [35,36,37,38,39,40,41,42]. Many of these are in the form of proteinaceous filaments with adhesin activity that mediate long-range adhesion during colonization [43,44,45,46]. Expression of these proteins may be regulated to match environmental conditions, which has significant implications for experimental studies of bacterial adhesion, i.e.…”

Localization of the bacterial agent of juvenile oyster disease (Roseovarius crassostreae) within affected eastern oysters (Crassostrea virginica)

“…In a previous study, we demonstrated that R. crassostreae have the unusual ability to produce unipolar fimbriae . These types of protein fibrils are important in other bacterial species for surface attachment (Wall and Kaiser, 1999) and the development of biofilms (O'Toole et al, 2000), or in the case of a pathogenic association, to host cells (Smyth et al, 1996). The molecular switch controlling the expression of flagella vs. fimbriae in R. crassostreae is unknown, however elucidation of this mechanism is expected to be important in understanding the early stages of JOD.…”