Type III secretion effectors in
bacterial genome
5 May 2010
Sūn Guăng Wén
Biochemistry, NUS
Melioidosis
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Causative agent: Burkholderia pseudomallei
Endemic area: SEA; northern Australia
Symptom: variable
Diagnosis: Serum test, culture of bacteria,
PCR
Risk factor: Type II diabetes and kidney
failure
Treatment: Ceftazidime
Vaccine: not available
Burkholderia pseudomallei
• Facultative anaerobic,
in soil and surface water
• Opportunistic pathogen
• Resistant to many antibiotics
• Huge genome: 4.1Mb +3.2Mb
• Many virulence factors: siderophore, flagella,
T3SSs, T6SSs
• Able to invade cells and survive intracellularly
Type III secretion system (T3SS)
SPI I of
Salmonella
T3SS and flagella
Distribution of T3SSs among pathogenic bacteria
Nat rev MCB 3:743
T3 Effectors modify host signaling pathways
Effectors mimic host protein function
Effectors can introduce covalentmodification
Effectors are less conserved
N-terminal of effector contains
secretion signal
Fusion assay
N-ter signal
reporter
Determination of secretion signal
http://www.effectors.org/
---very high false positive rate!
PLoS Pathogens April 2009 | Volume 5 | Issue 4 | e1000376
Signal is more defined within a
species
Inv/mxi/spa-like T3S3 of B. pseudomallei
Secreted effectors
Translocons
Base and inner membrane complex
Regulator
Molecular Microbiology (2002) 46(3), 649–659
Molecular Microbiology (2010) 76(3), 677–689
Chaperone
Burkholderia pseudomallei genome
Burkholderia pseudomallei K96243: NC_006350; NC_006351 ,
http://www.ncbi.nlm.nih.gov/sutils/genom_table.cgi
http://www.sanger.ac.uk/cgi-bin/blast/submitblast/b_pseudomallei
The challenge: To identify T3S3
effectors in bp genomes
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Define training sets, collect effector
sequences
Find patterns in N-terminals
Search Burkholderia pseudomallei
genomes
Blast top hits in protein databases
Verify through experiments
Assembly of T3S needle