Bacterial Secretion System Flashcards
What secretory systems are involved in inner membrane?
Sec and Tat
What secretory systems are involved in outer membrane?
T2SS and T5SS
What secretory systems are involved in both membranes?
T1SS, T3SS and T4SS
What can the Sec system be split into?
SecB pathway and SRP pathway
Summarise SecB pathway
Transports unfolded proteins across inner membrane!!!
Proteins secreted by SecB pathway contain signal sequence recognised by SecB protein
SecA binds to SecB and translocates complex to SecYEG channel
Secreted protein is folded in the periplasm
Summarise SRP pathway
Transports proteins to inner membrane!!!
SRP binds to protein when it is being translated by ribosomes
FtsY binds to complex and translocates it to SecYEG channel
Secreted protein remains in the inner membrane
Summarise Tat pathway
Transports folded proteins
Requires 3 proteins: Tat A B and C (Tat A & B are joined in g+)
Tat B and C bind a signal peptide of secretory protein
Tat A acts as a channel
What does T2SS require before it can secrete?
Protein secretion through inner membrane to periplasm via Tat or Sec pathway
Where is the T2SS found?
Channel in outer membrane only
What 4 parts make up T2SS?
Outer membrane complex
Periplasmic pseudopilus
Inner membrane platform
Cytoplasmic ATPase
What type of proteins does T5SS secrete?
Unfolded proteins, which have been secreted to periplasm using Sec pathway
What are the 3 types of T5SS?
Autotransporter secretion
Chaperone-usher secretion
Curli secretion
What is the Autotransporter Secretion System mechanism?
A single protein forms a tunnel (β-barrel) in the bacterial outer membrane. The functional part of the protein (passenger domain) travels through this tunnel to the outside.
How does the Chaperone-Usher Secretion System work?
Involves two proteins: the chaperone stabilizes pilus subunits inside the bacteria, and the usher assembles these subunits into pili on the bacterial surface
What is the Curli Secretion System?
Several proteins work together to make and assemble curli fibers (tiny threads) outside the bacteria
Why are autotransporters important for bacteria?
Autotransporters often act as virulence factors, including adhesins, toxins, and enzymes
What roles do chaperone-usher systems play in bacteria?
Essential for pilus formation, which facilitates bacterial adhesion and biofilm formation
How do curli fibers benefit bacteria?
Curli fibers contribute to biofilm formation, providing a protective environment for bacteria
What does Type 1 Secretory System (T1SS) transport?
Transports a variety of proteins, such as hemolysin in E. coli.
What are the components of T1SS?
- Inner Membrane Component (IMC): ATP Binding cassette transporter (ABC transporter) that recognizes specific protein motifs and uses ATP.
- Membrane Fusion Protein (MFP): Also known as Periplasmic Adaptor Protein, helps in substrate recognition.
- Outer Membrane Protein Channel: Forms a β-barrel in the outer membrane, e.g., TolC.
What is the Type III Secretory System (T3SS)?
Function: Acts like a needle and syringe to inject proteins into host cells.
Importance: Used by bacteria like Yersinia, Salmonella, and Shigella to secrete virulence factors
What are the components of T3SS?
Basal Body: Anchors the system and recruits substrates, with InvC acting as an ATPase.
Needle Component: Formed by PrgI protein, keeps substrate proteins unfolded.
Translocon: Rings formed by PrgK and PrgH in the inner membrane, and InvG in the outer membrane
What is the function and importance of the T4SS?
Function: Transports proteins and DNA-protein complexes to both prokaryotic and eukaryotic cells.
Importance: Related to bacterial conjugation systems
What is the Type IV Secretory System (T4SS)?
VirB/D System: Composed of 12 proteins (VirB1-11 and VirD4) with roles in forming translocon machinery, pili, and acting as ATPases.
Forms:
Pilus Biogenesis Form: VirB11 interacts with VirB4.
Substrate-Translocation Form: VirB11 interacts with VirD4.
