Chemistry Reference
In-Depth Information
17.1.1
Fimbriae/Pili
Fimbriae/pili are long surface polymers built up of various numbers of subunits
[1]. Usually, one major subunit (for example FimA or PapA of type 1 and type P
fi mbriae, respectively) forms the bulk of the shaft with minor subunits assisting
in fi mbriae assembly and lectin integration. The same type of fi mbria/pili may be
expressed by different types of bacteria. At the same time, the structure of fi mbria/
pili can vary within subclasses of bacteria based on the subunits supplying the
major building blocks. One example is enterotoxigenic
Escherichia coli
. These
bacteria express a number of different fi mbriae structures as illustrated in Figure
17.1. The structure of the P fi mbriae of uropathogenic
E. coli
is shown in the same
fi gure. Each bacterium harbors approximately 200- 500 fi mbriae.
The lectins are commonly presented at the tip of the fi mbriae/pili, but may also
be intercalated along the shaft. The carbohydrate specifi city of fi mbriae lectins
differs both within and between species. There are two reasons for this: (i) allelic
variants of fi mbriae/pili lectins of different bacteria and bacterial strains exhibit
minor structural variations; and (ii) the fi mbrial shaft itself appears to infl uence
the carbohydrate specifi city of the lectins.
Figure 17.1
A simplifi ed schematic represen-
tation of fi mbriae/pili of uropathogenic and
enterotoxigenic
E. coli.
(a) Fimbriae with the
lectin subunit placed at the top of the fi mbrial
rod (for example type P fi mbriae of uropatho-
genic
E. coli
). (b) Pili with the lectin activity
incorporated in the top major subunit (for
example CFA/I fi mbriae of enterotoxigenic
E. coli
). (c) Fimbriae with the lectin activity
intercalated along the shaft of the fi mbriae (for
example K88 of porcine enterotoxigenic
E. coli
).
Adapted from [27] .
