Lecture 14: Secretion systems

Question 1

Gram-negative vs Gram-positive cell walls

Answer 1

Gram-negative have a double membrane system. Outer and inner membrane. Inbetween the membranes is the murine layer. (peptidoglycan)
LPS on the outer leaflet of the outer membrane.

Gram-positive have only one membrane and a think murine layer.
Have LTA

Gram-negative have to overcome the double membrane for secretion. Insert secretion system

Question 2

General secretory pathway. (sec patheway)

Answer 2

pore in membrane to get proteins through
SecB: chaperone
SecA: ATPase
SecYEG: heterodimer channel

Question 3

General secretory pathway. (sec pathway)

Answer 3

pore in membrane to get proteins through
SecB: chaperone
SecA: ATPase
SecYEG: heterodimer channel

The protein requires a signal sequence to target it to the translocon.

Unfolded, post-translational
SPase cleaves the signal sequence off

Question 4

TAT pathway

Answer 4

twin-arginine translocation
fully translated - folded protein through TatA pore.

Proton pump-driven

Question 5

Co-translational transport

Answer 5

ribosome drives translocation 
SRP- signal recognition particle. 
N-terminus is targeted to FtsY receptor 
The N-terminus targets the SecYEG
The ribosome continues translation, which drives the protein through the SecYEG channel/pore. 

translation provides the energy for translocation.
can be used for proteins that are bound for integration into the membrane

Question 6

Secretion system 1-6

Answer 6

all gram-negative

Question 7

secretion systems 2 and 5 are_____

Answer 7

Not continuous. Sec and TAT pathway

Question 8

What secretion system is only in Gram-Positive bacteria, and why?

Answer 8

Secretion system 7. It only spans the inner membrane. The other SS all span the inner and outer membranes in Gram-negative.
Remember that SS 2 and 5 are discontinuous. Sec and TAT pathways across the inner membrane, and the type II and type V SS across the outer membrane

Question 9

What organism uses the same TAT pathway

Answer 9

Pseudomonas aeruginosa

Question 10

Type 2 and 5 SS

Answer 10

loading of the toxin (proteins) occurs in the periplasm space. ATPase used to drive the loaded protein up and out of the SS.