Biology Reference
In-Depth Information
Chapter 15
Type 3 secretion effectors
Abigail Clements, Cedric N. Berger, Mariella Lomma, Gad Frankel
Imperial College London, London, UK
INTRODUCTION
T3SS effector proteins of enterohemorrhagic
E. coli
(EHEC), enteropathogenic
E. coli
(EPEC) and
Shigella
affect diverse signaling pathways and physiologi-
cal processes when translocated into the host cell. For EPEC and EHEC seven
'core' effectors are encoded with the T3S translocation machinery on the locus of
enterocyte effacement (LEE) pathogenicity island (PI) (
McDaniel et al., 1995
),
while other effectors are encoded within prophages and other integrative ele-
ments (
Tobe et al., 2006
). Although EPEC and EHEC show high levels of conser-
vation between the LEE encoded effectors, there is significant diversity in their
non-LEE effector (NLE) repertoire; EPEC strains E2348/69 and B171 encode
at least 23 intact effector genes (
Iguchi et al., 2009
;
Deng et al., 2012
), whereas
the EHEC O157 strain Sakai is estimated to have closer to 50 T3SS effectors
(
Table 15.1
) (
Tobe et al., 2006
). The
Shigella
T3SS is encoded on a large viru-
lence plasmid along with the majority of identified T3SS effectors (
Table 15.2
).
Approximately 30
Shigella
T3SS effectors are currently recognized (
Parsot,
2009
) although as more
Shigella
isolates of different species are sequenced this
number may be revised. This chapter describes how these T3SS effectors modu-
late the host cytoskeleton, immune response, cell survival, and gut integrity.
CYTOSKELETON REMODELING
EPEC, EHEC and
Shigella
have acquired a subset of effectors to promote the
colonization of the host by modulating the host cytoskeleton. The molecular
mechanisms of pedestal formation, cell invasion, modulation of Rho GTPases
and reorganization of microtubules and intermediate filaments will be described.
Intimate attachment and pedestal formation
EHEC and EPEC colonization is characterized by the T3SS-dependent forma-
tion of attaching and effacing (A/E) lesions on the apical surface of enterocytes.
This presents as localized effacement of the microvilli (discussed further below),
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