Secretion Systems Flashcards
Why would bacteria need secretion systems?
- respond to its environment
- physiological processes
- none are constitutively active
Role of the Sec pathway in Gram + and archae
- translocation of proteins across the single plasma membrane
Role of the sec pathway in Gram -
- export of proteins into periplasm
How does Sec pathway work?
- machinery recognises a hydrophobic N-terminal leader sequence on proteins destined for secretion
- translocates across CM in unfolded state
- uses ATP hydrolysis and proton gradient for energy
- signal peptide is cleaved at protease cleavage site by Type 1 signal peptidase
- protein re-folds
What does Tat stand for?
Twin-arginine transport
How does Tat pathway work?
- recognises a motif rich in basic aa residues in the N-terminal region of large co-factor containing proteins
- translocates folded proteins
- uses only proton gradient as energy source
Sec-dependent secretion types
- Type V
- Type II
Sec-independent secretion types
- Type IV
- Type III
- Type I
Where are Type II systems found?
- only in Gram -ves
Main component of Type II systems
- translocation pore in OM
- 12-15 secretin subunits (large enough to accomodate folded protiens
4 components of Type II systems
- OM complex
- periplasmic pseudopilus
- IM platform
- cytoplasmic ATPase
Bacteria that use Type II system
- P. aeruginosa
- K. pneumoniae
What is the Type II IM platform made up of?
4 membrane proteins
- GspC, F,L,M
What makes the Type V system unique?
- substrate and secretion pore fuse to form a single polypeptide
2 domains of Type V autotransporters
- N-terminal passenger domain
- Conserved C-terminal domain (forms a transmembrane B-barrel pore)
Bacteria that use Type V system
- N. gonorrhoeae
- N. meningitides
Characteristics of Type I system
- secretion of large variety of substrates from cytoplasm to extracellular environment
- often assoc with nutrient acquisition and virulence
- closely related to resistance nodulation division (RND) family of multidrug efflux pumps
Describe Type 1 system channel
Tripartite double-membrane spanning channel
- ATP-binding cassette transporters (ABCs)
- Outer membrane protein (OMP)
- membrane fusion proteins (MFPs)
2 groups of ABC transporters in Type I system
- for large proteins from Gram -ves
- for small protiens and peptides
Components of Type I system
- TolC
- HlyD (MFP)
- HlyB (ABC)
Main component of Type III system
- Injectisome composed of 25 protiens organised into 2 main sub-strucatures
- double- membrane-spanning base composed of stacked rings
- needle-like filament protruding from bacterial surface into extracellular space
How is the Type IV system unique?
- can transport nucleic acids as well as proteins directly into host cells
Most common role of Type IV sytem
- to mediate conjugation of plasmid DNA
Examples of bacteria that use Type IV system
- H. pylori
- Rickettsia
- B. pertussis
Machinery of Type VI
2 main complexes
- membrane complex
- tail complex
Example of bacteria that use Type VI
- V. cholerae
- P. aeruginosa
