Biology Reference
In-Depth Information
Chapter 14
Type 3 secretion systems
Liam J. Worrall, Julien R.C. Bergeron, Natalie C.J. Strynadka
University of British Columbia, Vancouver, BC, Canada
INTRODUCTION
In 1994, the group of Hans Wolf-Watz observed that the pathogenic Gram-
negative bacterium
Yersinia pestis
could transfer toxin proteins (effectors)
directly into the cytoplasm of infected mammalian cells. Since this process was
independent from other secretion pathways known at the time, it was labeled
type 3 secretion (T3S) (
Salmond and Reeves, 1993
;
Rosqvist et al., 1994
).
A set of genes, organized in a complex operon structure, was shown to encode
for the proteins necessary and sufficient for the translocation of effectors
across both the bacterial membranes, as well as the mammalian cell membrane
(
Michiels et al., 1991
). This set of proteins was therefore called the type 3 secretion
system (T3SS).
Subsequently, homologous genes were identified in many human Gram-
negative pathogens such as
Salmonella enterica
spp.,
Burkholderia
spp.,
Chlamidia
spp.,
Pseudomonas aeruginosa
,
Vibrio parahaemolyticus
,
Shigella
spp., enterohemorrhagic
E. coli
(EHEC) and enteropathogenic
E. coli
(EPEC),
as well as in the plant pathogens
Pseudomonas syringae
,
Ralstonia sola-
nacearum
and
Erwinia chrysanthemi
. In most instances, the occurrence of T3S
was confirmed, and has been shown to be an important factor for pathogenic-
ity (for review, see
Troisfontaines and Cornelis, 2005
;
Coburn et al., 2007
;
Tampakaki et al., 2010
). The delivery of effector proteins into a host cell via
T3S allows the bacterium to manipulate the bacterial-host cell interaction in
its favor with effectors targeting a wide variety of cellular processes including
the cytoskeleton, phagocytosis, apoptosis, and the inflammatory response (see
Chapter 15).
The molecular basis for T3S was discovered in 1998, when
Kubori et al.
(1998)
observed the presence of syringe-shaped structures on the surface of
Salmonella typhimurium
. These possessed a morphology similar to the hook-
basal body organization of the bacterial flagellum, and were shown to be
composed of proteins encoded by the Pathogenicity Island 1 (SPI-1), a major
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