Secretion of flagellin by the LEE-encoded type III secretion system of enteropathogenic Escherichia coli.
BACKGROUND
Enteropathogenic Escherichia coli (EPEC) is an attaching and effacing (A/E) pathogen that possesses a type III secretion system (T3SS) encoded within the locus of enterocyte effacement (LEE). The LEE is essential for A/E lesion formation and directs the secretion and translocation of multiple LEE-encoded and non-LEE encoded effector proteins into the cytosol of infected cells. In this study we used proteomics to compare proteins exported to the culture supernatant by wild type EPEC E2348/69, a DeltaespADB mutant and a DeltaescF T3SS mutant.


RESULTS
We observed that flagellin was consistently and strongly present in the secretome of wild type EPEC and the DeltaespADB mutant but present only weakly in the secretome of the DeltaescF mutant. Given the ancestral relationship between the flagella export apparatus and virulence associated T3SSs, we investigated whether FliC could utilise the LEE-encoded T3SS for export. In the absence of a functional flagella export apparatus, we showed that FliC could be secreted by the LEE-encoded T3SS and stimulate (Toll-like receptor 5) TLR5 signalling but could not confer motility.


CONCLUSIONS
Since the secretion of FliC during A/E lesion formation would presumably be disadvantageous for the pathogen, we propose that virulence associated T3SSs and flagella T3SSs have evolved through a system of chaperones and complex regulatory pathways to be functional at different times to ensure that FliC secretion does not occur during T3SS effector translocation.
Badea
Luminita
L
Department of Microbiology, Monash University, Melbourne, Victoria, Australia. lbadea@unimelb.edu.au
Beatson
Scott A
SA
Kaparakis
Maria
M
Ferrero
Richard L
RL
Hartland
Elizabeth L
EL
D004269:DNA, Bacterial / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D054308:Enteropathogenic Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D005407:Flagella / Q000378:metabolism; D005408:Flagellin / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism*; D020543:Proteome / Q000378:metabolism; D040901:Proteomics; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D051198:Toll-Like Receptor 5 / Q000378:metabolism
D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C516095:FliC protein, E coli; C457340:LEE protein, E coli; D010750:Phosphoproteins; D020543:Proteome; D051198:Toll-Like Receptor 5; D005408:Flagellin