Molecular Strategies for Fimbrial Expression and Assembly

Abstract

Fimbriae or pili are long, filamentous, multimeric macromolecules found on the bacterial cell surface. Bacteria express a diverse array of fimbriae or pili that are involved in bacterial adherence and invasion. Fimbriae can be categorized based on their modes of expression and assembly. Type 1 fimbriae and P pili are distributed peritrichously and translocated to the cell surface by a chaperone/usher pathway. Type 4 pili are located at the pole of the cell and assembled via the type 11 secretion system. Curli fimbriae are coiled surface structures assembled by an extracellular nucleation/precipitation pathway. Fimbriae of oral Gram-negative and Gram-positive bacteria have not been well-studied as compared with the fimbriae of enteric pathogens. Oral pathogens, such as Eikenella corrodens, Actinobacillus actinomycetemcomitans, and Porphyromonas gingivalis, possess fimbriae that have been implicated in bacterial adhesion and invasion. These fimbriae are potential virulence factors in oral infectious processes. A. actinomycetemcomitans and E. corrodens have Type 4-like fimbriae, whereas P. gingivalis displays a unique type of fimbriae. To date, fimbriae of the oral primary colonizers, Actinomyces naeslundii and Streptococcus parasanguis, represent the only fimbriae characterized for any Gram-positive bacteria. The putative major fimbrial subunits, FimA and FimP of A. naeslundii and FapI of S. parasanguis, contain a signal sequence and cell-wall-sorting signal. The presence of extensive dipeptide repeats in FapI makes it unique among fimbrial molecules. Based on experimental data, a nucleation/precipitation pathway is proposed for fimbrial biogenesis of both S. parasanguis and A. naeslundii, although we cannot rule out an alternative covalent linkage model. The model systems described in this review served as a framework for hypotheses for how the known molecular factors of fimbriae on oral bacteria may be expressed and assembled.

FNR-Dependent RmpA and RmpA2 Regulation of Capsule Polysaccharide Biosynthesis in Klebsiella pneumoniae

“…Multiple virulence factors, including CPS, lipopolysaccharides, fimbriae, iron-acquisition system, porins, and antibiotic resistance factors, have been identified to be involved in K. pneumoniae infection. These virulence factors are processed or embedded in the cell envelope, thus allowing bacteria to internalize nutrients and adhere to diverse surfaces or niches within the human host for successful infection (Wu and Fives-Taylor, 2001; Kawai et al, 2011). Of these virulence factors, CPS is considered the major determinant of K. pneumoniae pathogenesis (Sahly et al, 2000; Lin et al, 2004).…”

Pangenome and immuno-proteomics analysis of Acinetobacter baumannii strains revealed the core peptide vaccine targets

“…Another factor, pili assembly chaperone is engaged in crucial steps of cell wall organization, chaperone mediated protein folding and pilus organization [ 99 ]. Similarly, P pilus assembly protein is a fimbrial usher protein and involves in transporter activity [ 100 ]. The molecular function of one of the important core vaccine candidate, PonA involves selective and non-covalent binding of any antibacterial drug which contains the condensed beta-lactam thiazolidine ring system [ 101 ].…”

Porphyromonas gingivalis fimbriae

“…The primary protein sequences of FimA share no significant homology with other described fimbrial proteins, indicating that P. gingivalis may possess a unique class of fimbria subunits (2, 36, 37, 39, 50). …”

“…These structures have been classified as major or long fimbriae (FimA), based on their fimbrillin monomer composition, and range in size from 41 to 49 kDa (34–36). Even though ultrastructural studies were introduced 30 years ago, such examinations are still often used in combination with others for revealing additional information about this species (37).…”