title: SepD/SepL-dependent secretion signals of the type III secretion system translocator proteins in enteropathogenic Escherichia coli.
abstract: The type III protein secretion system (T3SS) encoded by the locus of enterocyte effacement (LEE) is essential for the pathogenesis of attaching/effacing bacterial pathogens, including enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and Citrobacter rodentium. These pathogens use the T3SS to sequentially secrete three categories of proteins: the T3SS needle and inner rod protein components; the EspA, EspB, and EspD translocators; and many LEE- and non-LEE-encoded effectors. SepD and SepL are essential for translocator secretion, and mutations in either lead to hypersecretion of effectors. However, how SepD and SepL control translocator secretion and secretion hierarchy between translocators and effectors is poorly understood. In this report, we show that the secreted T3SS components, the translocators, and both LEE- and non-LEE-encoded effectors all carry N-terminal type III secretion and translocation signals. These signals all behave like those of the effectors and are sufficient for mediating type III secretion and translocation by wild-type EPEC and hypersecretion by the sepD and sepL mutants. Our results extended previous observations and suggest that the secretion hierarchy of the different substrates is determined by a signal other than the N-terminal secretion signal. We identified a domain located immediately downstream of the N-terminal secretion signal in the translocator EspB that is required for SepD/SepL-dependent secretion. We further demonstrated that this EspB domain confers SepD/SepL- and CesAB-dependent secretion on the secretion signal of effector EspZ. Our results thus suggest that SepD and SepL control and regulate secretion hierarchy between translocators and effectors by recognizing translocator-specific export signals.
  
  
  OBJECTIVE
  Many bacterial pathogens use a syringe-like protein secretion apparatus, termed the type III protein secretion system (T3SS), to secrete and inject numerous proteins directly into the host cells to cause disease. The secreted proteins perform different functions at various stages during infection and are classified into three substrate categories (T3SS components, translocators, and effectors). They all contain secretion signals at their N termini, but how their secretion hierarchy is determined is poorly understood. Here, we show that the N-terminal secretion signals from different substrate categories all behave the same and do not confer substrate specificity. We further characterize the secretion signals of the translocators and identify a translocator-specific signal, demonstrating that substrate-specific secretion signals are required in regulating T3SS substrate hierarchy.
authors: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada.
authors: Wanyin
authors: W
authors: Deng
authors: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada.
authors: Hong B
authors: HB
authors: Yu
authors: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada.
authors: Yuling
authors: Y
authors: Li
authors: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada bfinlay@msl.ubc.ca.
authors: B Brett
authors: BB
authors: Finlay
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D054308:Enteropathogenic Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D006367:HeLa Cells; D006801:Humans; D005810:Multigene Family; D015398:Signal Transduction / Q000502:physiology; D013379:Substrate Specificity
chemical_list: D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C495684:SepD protein, E coli; C416081:SepL protein, E coli
references: J Bacteriol. 2009 Jan;191(1):347-54
references: 18952797
references: Mol Microbiol. 2008 Sep;69(6):1499-512
references: 18673458
references: Proc Natl Acad Sci U S A. 2009 Oct 20;106(42):17939-44
references: 19815525
references: Nat Rev Microbiol. 2010 Jan;8(1):26-38
references: 19966814
references: J Bacteriol. 2010 Jan;192(2):525-38
references: 19897651
references: J Biol Chem. 2010 Feb 26;285(9):6790-800
references: 20034934
references: Mol Microbiol. 2010 Feb;75(4):924-41
references: 20487288
references: Science. 2010 May 21;328(5981):1040-3
references: 20395475
references: J Bacteriol. 2010 Jul;192(13):3534-9
references: 20400543
references: J Bacteriol. 2010 Aug;192(15):3847-9
references: 20525826
references: J Bacteriol. 2010 Nov;192(22):6093-8
references: 20833800
references: Mol Biosyst. 2010 Dec;6(12):2448-58
references: 20877914
references: Infect Immun. 2011 Jan;79(1):23-32
references: 20974833
references: Science. 2011 Mar 4;331(6021):1188-91
references: 21292939
references: Science. 2011 Mar 4;331(6021):1147-8
references: 21385706
references: J Bacteriol. 2011 Jun;193(12):2972-80
references: 21498649
references: Mol Microbiol. 2011 Jun;80(6):1420-38
references: 21488979
references: J Bacteriol. 2011 Dec;193(23):6683-700
references: 21965570
references: MBio. 2012;3(1). pii: e00243-11. doi: 10.1128/mBio.00243-11
references: 22334517
references: Microbiol Mol Biol Rev. 2012 Jun;76(2):262-310
references: 22688814
references: Mol Cell Proteomics. 2012 Sep;11(9):692-709
references: 22661456
references: Mol Microbiol. 2012 Dec;86(6):1464-81
references: 23121689
references: Cell Rep. 2013 Mar 28;3(3):709-15
references: 23523349
references: J Bacteriol. 2013 May;195(10):2119-25
references: 23396917
references: Annu Rev Microbiol. 2014;68:415-38
references: 25002086
references: Proc Natl Acad Sci U S A. 2006 Oct 3;103(40):14941-6
references: 16990433
references: J Bacteriol. 2000 Nov;182(22):6490-8
references: 11053395
references: Infect Immun. 2001 Jun;69(6):4055-64
references: 11349076
references: J Bacteriol. 2002 Sep;184(17):4699-708
references: 12169593
references: Mol Microbiol. 2002 Aug;45(4):905-16
references: 12180912
references: Annu Rev Cell Dev Biol. 2002;18:107-33
references: 12142275
references: Mol Microbiol. 2002 Nov;46(3):855-68
references: 12410841
references: Infect Immun. 2003 Jun;71(6):3310-9
references: 12761113
references: Microbiology. 2003 Aug;149(Pt 8):2093-106
references: 12904549
references: Arch Microbiol. 2003 Sep;180(3):218-26
references: 12856107
references: Microbiology. 2003 Dec;149(Pt 12):3639-47
references: 14663095
references: Proc Natl Acad Sci U S A. 2004 Mar 9;101(10):3597-602
references: 14988506
references: Nat Rev Microbiol. 2004 Feb;2(2):123-40
references: 15040260
references: Mol Microbiol. 2004 Jun;52(6):1613-25
references: 15186412
references: J Bacteriol. 2004 Aug;186(16):5486-95
references: 15292151
references: Mol Microbiol. 2004 Nov;54(3):604-19
references: 15491354
references: Proc Natl Acad Sci U S A. 1995 Dec 19;92(26):11998-2002
references: 8618831
references: Science. 1997 Nov 7;278(5340):1140-3
references: 9353199
references: Infect Immun. 2005 Apr;73(4):2135-46
references: 15784556
references: Infect Immun. 2005 Jul;73(7):4327-37
references: 15972527
references: Infect Immun. 2006 Feb;74(2):810-20
references: 16428723
references: Mol Cell. 2006 Mar 3;21(5):653-64
references: 16507363
references: Nat Rev Microbiol. 2006 Nov;4(11):811-25
references: 17041629
references: EMBO J. 2007 Jun 20;26(12):3015-24
references: 17510628
references: J Bacteriol. 2008 Mar;190(6):2221-6
references: 18178741
references: Cell Host Microbe. 2008 Feb 14;3(2):104-13
references: 18312845
references: Nature. 2008 May 1;453(7191):124-7
references: 18451864
references: BMC Microbiol. 2008;8:134
references: 18681975
references: Mol Microbiol. 2009 Jan;71(2):449-60
references: 19017268