Enteropathogenic Escherichia coli (EPEC) Tir receptor molecule does not undergo full modification when introduced into host cells by EPEC-independentmechanisms
B. Kenny et J. Warawa, Enteropathogenic Escherichia coli (EPEC) Tir receptor molecule does not undergo full modification when introduced into host cells by EPEC-independentmechanisms, INFEC IMMUN, 69(3), 2001, pp. 1444-1453
Enteropathogenic Escherichia coli (EPEC), like many other gram-negative pat
hogens, encodes a type III secretion apparatus dedicated to the release of
virulence-associated proteins. One such protein, Tir, is translocated into
host cells, where it is modified by the addition of phosphate groups, resul
ting in a number of species with distinct molecular mass. One phosphorylati
on event, on tyrosine residue 474 of Tir, does not contribute to shifts in
molecular mass but is essential for its actin-nucleating function. The role
of the nonphosphotyrosine related modifications is unknown. In this paper,
we demonstrate, using three different approaches, that Tir does not encode
sufficient information to facilitate its complete modification when introd
uced into host cells in EPEC-independent mechanisms. Each system revealed t
hat Tir is a substrate for a host kinase whose action results in its partia
l modification to a form similar to one evident in EPEC-infected host cells
. Further Tir modification could not be induced by infecting cells with EPE
C, suggesting that Tir must be coexpressed with other EPEC factors to enabl
e its full modification within host cells. One approach used Yersinia spp.
to deliver Tir into host cells, and this system revealed that Tir secretion
and translocation can occur in the absence of the Tir chaperone molecule,
CesT (formerly known as OrfU). CesT was found to be an efficiency factor wh
ich was not required, unlike in EPEC, for Tir stability, indicating that it
may function to guide Tir to the translocation apparatus or maintain it in
a secretion-competent form.