Chemistry Reference
In-Depth Information
preferentially to globotetraosylceramide (Gb4), a major glycolipid of human kidney
and urether. The third class, present in fi mbriae with a P - related sequence ( Prs ),
binds mainly to the Forssman antigen but also to GloboA, and is commonly found
in canine
E. coli
isolates. However, this G-protein class has also been associated
with human cystitis.
17.1.1.3
Type S Fimbriae
The S fi mbria [1] is produced only by a limited number of
E. coli
strains. It is
strongly associated with meningitis in newborns, with 80% of the isolated strains
being S - fi mbriated. The lectin specifi city is encoded by the SfaS subunit that
exists in two forms: SfaS-I and -II. The former has been cloned from uropatho-
genic
E. coli
isolates, while the latter was cloned from meningitis- associated
E. coli
isolates. SfaS binds to
2,3-sialylated galactose on glycoproteins and possibly
also glycolipids. One identifi ed ligand for SfaS- II is fi bronectin of interstitial con-
nective tissues and extracellular matrices [4]. The protein carries
α
2,3 - sialylated
galactose on
N
-glycans, and is found mainly in developing basement membranes
of embryonic tissues and on vascular endothelial cells of adults. It is believed that
S fi mbriae mediate targeting of meningitis- associated
E. coli
to the epithelium and
endothelium of the choroid plexus, which is the portal entry into the cerebrospinal
fl uid.
α
17.1.1.4
Type IV Pili
This pilin is expressed by a number of different bacteria and exists in two forms:
type IVa and IVb [1, 5]. The difference between the two pili is the folding of the
β
-helices. Type IVa is expressed by
Pseudomonas aeru-
ginosa
(for pathogenicity, see Section 17.1.2.2 ) and
Neisseria gonorrhoeae.
The car-
bohydrate binding activity of
P. aeruginosa
type IV pili is encoded in the C-terminal
region of the major subunit of the pili, PilA, but it is only exposed for ligand
binding at the top of the pilin. This is in contrast to most fi mbriae where the lectin
activity is encoded by a distinct minor subunit. The carbohydrate ligands of
P. aeruginosa
type IV pili are the glycosphingolipids asialo-GM1 and asialo-GM2
on epithelial cells.
N. gonorrhoeae
shares the specifi city for human epithelial cells
with
P. aeruginosa.
However, no carbohydrate ligand has been identifi ed. Type IVb
pili are expressed by
Vibrio cholerae
and enteropathogenic
E. coli
. The pilin of the
former is also known as mannose-sensitive hemagglutinin, while the ligand for
enteropathogenic
E. coli
on epithelial cells might be
N
- acetyllactosamine, a common
ligand for galectins
in situ
(for information on galectin ligands, please see Table
19.3, on the common fold Figure 13.2 ).
-sheets that surround the
α
17.1.2
Bacterial Surface Lectins
Bacterial lectins can also be presented directly on the bacterial surface and as such
mediate adhesion to host cells.
Helicobacter pylori
and
P. aeruginosa
are two exam-
ples of this as described below.
