Bacterial Pili (i)
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Note on Pili (Part I) S. Saengamnatdej, Ph.D. •
Overview: •
Pilus shaft (or fimbrial rod) : contains hundreds (or thousands) of protein subunits (called pilin, 15-25 kDa).
•
Important virulence factors (in UT, GI, genital infections).
•
Targets for vaccination.
•
Have adhesive structure •
Adhesins •
at the tip of pili (hair) or fimbriae (thread or fiber)
•
behave as lectins
•
their ligands = cell receptor (Oligosaccharide residues of glycoprotein or glycolipid receptors)
•
also bind to structural elements of the basement membrane (collagen, fibronectin, etc.)
•
Functions •
Site for phage attachment
•
DNA transfer
•
Biofilm formation
•
Cell aggregation
•
Cell invasion
•
Motility (twitching)
Pili of G(-) bacteria •
Structure typically: non-covalent homopolymerization of pilins (form the pilus shaft)
•
Classified into 4 groups (depend on assembly pathways). 1. Pili with chaperone-usher pathway. 1. Assembly: •
The pilin is secreted into the periplasmic space. In there, it binds to specific a chaperone (FimC) which helps protein folding & prevents premature assembly. The complex is then delivered to the outer membrane usher, which serves as a platform for pilus assembly. Adhesive structures: (1.) heteropolymers, flexible fibrillar tip, with a single specific adhesive protein at the end. (2.)
homopolymers of non-pilus adhesins 2. Members •
Type I : •
found in Enterobacteriaceae & in most E. coli strains
•
is most prevalent type of pilus in uropathogenic
Escherichia coli (UPEC) adhesive structure (adhesion causes cystitis). •
encoded by the fim gene cluster (fimA-fimH).
•
helical rod (right-handed helical array of 500-3000 copies of FimA) with the size of 6.9 nm thick x 1-2 micrometers long is connected via FimF to a short stubby 3 mm wide linear tip fibrillum containing FimG and the specific adhesin FimH (Fig.1 below)
•
FimH has 2 domains: receptor-binding domain (Nterminal) & pilin domain (C-terminal).
•
FimH binds to mannose-containing receptors. (uroplakins; integral glycoprotein receptors coating luminal surface of bladder epithelium.)
•
FimH binding to bladder cells triggers a signal transduction cascade (leading to actin reorganization, phosphoinositide-3-kinase activation and protein tyrosine phosphorylation).
•
Type I pili are required for initial surface attachment in biofilm formation.
•
P pili •
UPEC.
•
Virulent factor (pyelonephritis).
•
Encoded by 11 pap genes (pyelonephritis-associated pili genes).
•
Structure similar to type I pili. •
Rod (a right-handed helical cylinder) with the dimension of 6.8 nm wide x many micrometers long have PapG adhesin (and three minor pilus proteins PapE, PapF, and PapK) on the tip of fibrillum.
•
Three PapG variants (PapGI, -II, and -III) have different
receptor specificity, binding preferentially to globotriaosylceramide or GbO3 (abundant on human uroepithelial cells), globoside or GbO4 (glycolipid isoreceptor of the human kidney, primarily associated with human pyelonephritis & bacteremia), and Forssman antigen or globopentosylceramide, GbO5, (associated with cystitis), respectively
•
•
flexible tip fibrillum
•
has 2 domains (see Fig. 2)
S pili •
in E. coli causing sepsis, meningitis, & UTI.
•
SfaS adhesin binds to SA on endothelial cells & to kidney epithelial cell receptors.
•
major SfaA pilins have adhesive properties binding to glycolipids & plasminogen.
•
Hif pili •
•
•
in Haemophilus influenza
PMF (Proteus mirabilis fimbriae) pili •
in Proteus mirabilis (cystitis & polynephritis).
•
pmf operon encodes 5 predicted proteins •
PmfA (major pilin)
•
PmfC (usher)
•
PmfD (chaperone)
•
PmfE (minor pilin)
•
PmfF (adhesin)
Dr/ Afa adhesin family pili •
with homopolymer adhesin
•
in UPEC
•
in diffusely adhering E. coli (DAEC)
•
encoded by at least 5 afa genes (A-E)
•
AfaE is adhesin
•
most Afa/Dr adhesins recognize DAF (a complementregulatory membrane protein, on RBC, uroepithelium, and CEACAMs). Fig. 3.
•
AfaE-I, AfaE-III, DraE and DaaE have 2 independently
functional binding sites. •
DraE (not AfaE-III, a homologue) binds to Type IV collagen.
•
may facilitate ascending colonization & chronic infection of UT.
•
some associated with enteric infection.
•
facilitate UPEC invasion of uroepithelial cells.
•
AfaD adhesin has invasin properties.
•
Dr fimbriae can be released into medium (in response to temperature & reduced oxygen).
•
F1 pili •
in Yersinia pestis •
•
in ETEC (enterotoxigenic E. coli) •
•
F1 (polymeric capsular antigen) CFA/I (colonization factor antigen I)
Others (K99, K88, F17, or F6 pili) •
thinner fibers (2-5 nm thick).
•
mostly associated with animal ETEC.
2. Type IV pili (more details from here onwards, will be continued on a new page; part 2). 3. Pili with extracellular nucleation/precipitation pathway (curli pili) 4. Pili with alternative chaperone-usher pathway (CS1 pilus family)
Figure 1 Type I Pilus (note: FimC = chaperone, FimD = usher) (Michael Vetsch, et al, 2004) see http://www.nature.com/nature/journal/v431/n7006/images/nature02891-f1.2.jpg
Figure 2 FimH and PapG (Source: Steve Matthews, Biological Nuclear Magnetic Resonance (NMR)) http://www.bio.ic.ac.uk/research/matthews/papg.jpg
Figure 3 DraE/AfaE Adhesin (green = DAF-binding site, red = CEA-binding site) (Korotkova et al, 2004) http://www.jbc.org/content/vol281/issue39/images/medium/zbc0410669330007.gif
Overview: •
Pilus shaft (or fimbrial rod) : contains hundreds (or thousands) of protein subunits (called pilin, 15-25 kDa).
•
Important virulence factors (in UT, GI, genital infections).
•
Targets for vaccination.
•
Have adhesive structure •
Adhesins •
at the tip of pili (hair) or fimbriae (thread or fiber)
•
behave as lectins
•
their ligands = cell receptor (Oligosaccharide residues of glycoprotein or glycolipid receptors)
•
also bind to structural elements of the basement membrane (collagen, fibronectin, etc.)
•
Functions •
Site for phage attachment
•
DNA transfer
•
Biofilm formation
•
Cell aggregation
•
Cell invasion
•
Motility (twitching)
Pili of G(-) bacteria •
Structure typically: non-covalent homopolymerization of pilins (form the pilus shaft)
•
Classified into 4 groups (depend on assembly pathways). 1. Pili with chaperone-usher pathway. 1. Assembly: •
The pilin is secreted into the periplasmic space. In there, it binds to specific a chaperone (FimC) which helps protein folding & prevents premature assembly. The complex is then delivered to the outer membrane usher, which serves as a platform for pilus assembly. Adhesive structures: (1.) heteropolymers, flexible fibrillar tip, with a single specific adhesive protein at the end. (2.)
homopolymers of non-pilus adhesins 2. Members •
Type I : •
found in Enterobacteriaceae & in most E. coli strains
•
is most prevalent type of pilus in uropathogenic
Escherichia coli (UPEC) adhesive structure (adhesion causes cystitis). •
encoded by the fim gene cluster (fimA-fimH).
•
helical rod (right-handed helical array of 500-3000 copies of FimA) with the size of 6.9 nm thick x 1-2 micrometers long is connected via FimF to a short stubby 3 mm wide linear tip fibrillum containing FimG and the specific adhesin FimH (Fig.1 below)
•
FimH has 2 domains: receptor-binding domain (Nterminal) & pilin domain (C-terminal).
•
FimH binds to mannose-containing receptors. (uroplakins; integral glycoprotein receptors coating luminal surface of bladder epithelium.)
•
FimH binding to bladder cells triggers a signal transduction cascade (leading to actin reorganization, phosphoinositide-3-kinase activation and protein tyrosine phosphorylation).
•
Type I pili are required for initial surface attachment in biofilm formation.
•
P pili •
UPEC.
•
Virulent factor (pyelonephritis).
•
Encoded by 11 pap genes (pyelonephritis-associated pili genes).
•
Structure similar to type I pili. •
Rod (a right-handed helical cylinder) with the dimension of 6.8 nm wide x many micrometers long have PapG adhesin (and three minor pilus proteins PapE, PapF, and PapK) on the tip of fibrillum.
•
Three PapG variants (PapGI, -II, and -III) have different
receptor specificity, binding preferentially to globotriaosylceramide or GbO3 (abundant on human uroepithelial cells), globoside or GbO4 (glycolipid isoreceptor of the human kidney, primarily associated with human pyelonephritis & bacteremia), and Forssman antigen or globopentosylceramide, GbO5, (associated with cystitis), respectively
•
•
flexible tip fibrillum
•
has 2 domains (see Fig. 2)
S pili •
in E. coli causing sepsis, meningitis, & UTI.
•
SfaS adhesin binds to SA on endothelial cells & to kidney epithelial cell receptors.
•
major SfaA pilins have adhesive properties binding to glycolipids & plasminogen.
•
Hif pili •
•
•
in Haemophilus influenza
PMF (Proteus mirabilis fimbriae) pili •
in Proteus mirabilis (cystitis & polynephritis).
•
pmf operon encodes 5 predicted proteins •
PmfA (major pilin)
•
PmfC (usher)
•
PmfD (chaperone)
•
PmfE (minor pilin)
•
PmfF (adhesin)
Dr/ Afa adhesin family pili •
with homopolymer adhesin
•
in UPEC
•
in diffusely adhering E. coli (DAEC)
•
encoded by at least 5 afa genes (A-E)
•
AfaE is adhesin
•
most Afa/Dr adhesins recognize DAF (a complementregulatory membrane protein, on RBC, uroepithelium, and CEACAMs). Fig. 3.
•
AfaE-I, AfaE-III, DraE and DaaE have 2 independently
functional binding sites. •
DraE (not AfaE-III, a homologue) binds to Type IV collagen.
•
may facilitate ascending colonization & chronic infection of UT.
•
some associated with enteric infection.
•
facilitate UPEC invasion of uroepithelial cells.
•
AfaD adhesin has invasin properties.
•
Dr fimbriae can be released into medium (in response to temperature & reduced oxygen).
•
F1 pili •
in Yersinia pestis •
•
in ETEC (enterotoxigenic E. coli) •
•
F1 (polymeric capsular antigen) CFA/I (colonization factor antigen I)
Others (K99, K88, F17, or F6 pili) •
thinner fibers (2-5 nm thick).
•
mostly associated with animal ETEC.
2. Type IV pili (more details from here onwards, will be continued on a new page; part 2). 3. Pili with extracellular nucleation/precipitation pathway (curli pili) 4. Pili with alternative chaperone-usher pathway (CS1 pilus family)
Figure 1 Type I Pilus (note: FimC = chaperone, FimD = usher) (Michael Vetsch, et al, 2004) see http://www.nature.com/nature/journal/v431/n7006/images/nature02891-f1.2.jpg
Figure 2 FimH and PapG (Source: Steve Matthews, Biological Nuclear Magnetic Resonance (NMR)) http://www.bio.ic.ac.uk/research/matthews/papg.jpg
Figure 3 DraE/AfaE Adhesin (green = DAF-binding site, red = CEA-binding site) (Korotkova et al, 2004) http://www.jbc.org/content/vol281/issue39/images/medium/zbc0410669330007.gif
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