Prokaryotic Protein Secretion Systems Flashcards
True or false, not all protein secretion systems require energy
False, they all do
What is placed onto most proteins needed to be secreted by the cell?
N-terminus signal peptides
What does each signal peptidase do?
SP1 - cleaves off the signal peptide of almost all proteins
SP2 - cleaves off the signal peptide of Lipo Proteins
Are signal peptides conserved molecules?
No, but there are three conserved area’s.
Explain the three conserved area’s of signal peptides
1) (+) N region terminus (n region)
2) hydrophobic core (h region)
3) (-) C Terminus which is also hydrophilic (c region)
Explain Lipoprotein signal peptides
- also have c, n , h region
- has a LIPO box region which contains a positive cysteine group
- this cysteine group must be lipid modified before the SP is cleaved
- is monitored by SP 2
where are signal peptides cleaved in lipoproteins?
just before the fatty acid cysteine that is apart of the LIPO box
Explain the SEC dependent pathway
- proteins needed to be secreted are made as precursor proteins with a N - terminal signal peptide
- signal peptides delay the folding of the protein
- chaperone proteins maintain the unfolded precursor
- Translocon in PM transfers the protein through the PM and uses SP 1 or 2 to cleave signal peptide
What is the GSP?
General secretion pathway. This is the same thing as SEC dependent pathway
How far can the GSP get a protein?
only through the PM and into the periplasm
What is the SEC system?
The system to get a protein into the periplasm
What is SecB?
the cytoplasmic chaperone protein that keeps the precursor protein unfolded and stable
What is SecA?
just an ATPase that provides energy for export
What proteins form the channel complex to secrete the new protein?
Sec Y, E, G
What is Post-translational secretion?
Entire protein is synthesized before translocation. E.g the Brauns lipo protein in gram negative cells
What is Co-translational secretion?
synthesis occurs at the same time as secretion
What part of the protein enters the Sec pathway first?
the N terminus in most pathways. This is because the signal peptide is located on it. If the signal peptide was some how on the C - terminus then Co-translational secretion is impossible.
What is the high affinity SecA binding site?
Sec Y and Sec E of the channel
Explain what the type 2 secretion system achieves and what it secretes?
- type 2 secretion gets proteins past the periplasm and through the Outer Membrane
- uses SEC SYSTEM to get proteins into periplasm therefore sec dependent
- many pathogens use Type 2 to secrete toxins, proteases, and lipase’s
Most of the the Type 2 secretion proteins are OMP’s. T or F
false, most are PM integral proteins
What is the only component in the OM for type 2 secretion?
Secretin
How does the type 2 secretion system get proteins out of OM (3)
- secretin forms pore in OM
- Several integral proteins form and miniature type IV pilus called a piston
- addition of subunits and extraction of subunits extends and pulls back piston to shove out protein through Secretin
what are pseudopilins?
integral proteins homologous to type IV pili. There are 5 involved in type 2 secretion. These form the actual piston
Explain what Type 1 secretion system achieves? (3)
- exports proteins as a complete protein through both the PM and OM
- therefore SEC INDEPENDENT
- proteins have signal on C terminus therefore this is always post-translational secretion
