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*Type III secretion systems
- found on pathogenicity islands and associated with virulence
- not found on non-pathogenic members of same species
- *proteins are highly conserved
- diversity in the secreted proteins from one strain
- often the pathogenicity island encodes the type III apparatus, secreted proteins, chaperones and regulators
- have intricate syringe-needle complex
- conformational change translocates proteins
- very fast
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effectors
- type II secreted proteins
- can be in pathogenicity island or outside but secreted via TTSS
- typically associated with invasion and/or modulate of host function
- typically shared regulation
- suppress defense and promote virulence
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*identification of type III effectors
- expression induced by HrpL sigma factor
- presence of hrp-box in promoters
- N-terminal TTSS signal peptide (ser rich, aliphatic aa in position 3 or 4, not acidic aa's in first 12 aa's)
- delivery into hosts by TTSS
- often have eukaryotic (host) targeting sequences
- in order for bacterial effector to go to correct subcellular locale, must have target sequence
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enteropathogenic E. coli (EPEC)
- type III secretion of its own receptor
- host can evolve so that it is not recognized by pathogen
- EPEC uses TTSS to deliver effector named TIR to the host cell where is then acts as receptor for intimin facilitating adhesion and pedestal formation
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Type IV secretion
- uses proteins that resemble the conjugation machinery to secrete proteins and/or DNA from either the cytoplasm or periplasm
- used to transfer bacterial DNA to host
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*T-DNA
- requires T4SS for translocation of T-DNA complex into plant cell - thought
- that the T-DNA travels through the T-Pilus, autoinducers promote T-DNA
- transfer
- integrated T-DNA contains genes to make a modified amino acid
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