Biology Reference
In-Depth Information
TABLE 6.2
ETEC colonization factors—cont'd
Colonization
factor
Structure
GenBank ref
Reference(s)
CS10 (antigen
2230)
Non-fimbrial
Darfeuille-Michaud et al.,
1986
CS11 (PCFO148)
Thin curly fibrils
∼
3 nm
Knutton et al., 1987
CS12 (PCFO159)
Fimbriae
Tacket et al., 1987
CS22
Thin fibrils
Pichel et al., 2000
CS23
Non-fimbrial
Del Canto et al., 2012
Additional uncharacterized antigens with sequence homology to CS20 (
Nada et al., 2011
).
The molecular and structural biology of CFA/I pilus biogenesis has been
described in some detail (
Jordi et al., 1992
;
Li et al., 2009
). This pilus belongs to
the chaperone-usher family of adhesive organelles (see Chapter 12). The plas-
mid-encoded CFA/I operon encompasses genes for CfaA a putative chaperone,
CfaB the major fimbrial structural subunit, CfaC a putative outer membrane
usher protein, and CfaE, the minor pilin tip adhesin subunit (
Baker et al., 2009
).
The assembled CFA/I pili are approximately 1 µm in length with approximately
1000 CfaB subunits polymerized into the shaft to present single CfaE subunits
as the tip adhesin. Intriguingly, in a spring-like fashion (
Mu et al., 2008
), CFA/I
can assume both tightly wound helical structures or more relaxed open states in
response to shear stress, perhaps permitting enhanced adhesion in response to
intestinal flow (
Andersson et al., 2012
).
Plasmid CF loci encode a wide variety of proteinaceous structures that
assume the shape of fimbriae, fibrils, helical, or afimbrial surface molecules
(
Wolf, 1997
;
Qadri, et al., 2005
). Since the discovery of CFA/I, new CFs con-
tinue to be identified, with more than 25 antigenically distinct factors described
to date (
Qadri et al., 2005
). On average the fimbrial structures described to date
are on the order of 1-2 µm in length. Distinct from these structures is a type IV
pilus referred to as longus that extends to more than 20 µm from the bacterial
surface (
Giron et al., 1994
). LngA
,
the major structural pilin subunit of longus,
also known as CS20, is recognized during ETEC infections (
Qadri et al., 2000
)
and shares significant N-terminal homology with other type-4 pilins including
those which comprise the toxin co-regulated pilus (TCP) of
V. cholerae
and the
bundle forming pili of enteropathogenic
E. coli
(see Chapter 13) (
Giron et al.,
1997
)
.
Interestingly, intestinal colonization and adherence are complex pheno-
types that involve multiple genes in addition to the classic colonization factors.
Studies implicating LT in promoting epithelial cell adherence (
Johnson et al.,
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