Secretion systems

Question 1

Sec translocase basics

Answer 1

transports unfolded proteins into periplasmic space
g- and g+
signal tag is at N-terminus
protein is funnelled through SecYEG protein
Tag is cut off by signal peptidase after translocation

Question 2

Sec translocase types

Answer 2

co-translational: secretion tag recognised by signal recognition particle (SRP) as the protein is being translated
post-translational: signal tag recognised by SecB after translation is complete

Question 3

Tat translocase

Answer 3

g+ and g-
exports folded proteins
recognition sequence is a twin arginine tag at the N-terminus
recognition of tag by TatB and C triggers the formation of the Tat A ring tag is removed by signal peptidase I

Question 4

T1SS

Answer 4

Single step
crosses 2 membranes
for large, unfolded proteins
3 proteins make a channel (HlyB, D and Tol C)
secreted proteins have C-terminus secretion signal

Question 5

T5SS steps

Answer 5

Multi step
1. translocation of protein into periplasmic space by Sec translocase
2. signal tag removed
3. shredded through BAM complex - translocation domain removed
4. protein is cleaved and released or anchored to surface

Question 6

T5SS protein

Answer 6

N-terminal signal tag
cargo domain (protein)
linker
translocator domain

Question 7

T3SS example

Answer 7

EPEC
translocates Tir into host cell to create a pedestal

Question 8

T3SS, what is and proteins

Answer 8

contact dependent
translocates effectors into host cell
molecular syringe
effector proteins have a N-terminal sequence, which can be bound by chaperones

Question 9

what is the T3SS homologous to

Answer 9

flagella biosynthesis and assembly systems

Question 10

T4SS

Answer 10

Translocates proteins and DNA to other bacteria or eukaryotic cells
two subfamilies:
conjugation machinery via VirB/VirD
protein transfer via Dot/Icm system

Question 11

T4SS: VirB/VirD example

Answer 11

transports DNA + proteins
in agrobacterium, delivers fragment of their genome plus effector proteins that lead to crown gall disease
delivers DNA with a pilus (VirB)

Question 12

Dot/Icm example

Answer 12

translocation of effector proteins into the cytoplasm of host cells
used by intracellular pathogens Legionella pneumophila and coxiella burnetii
translocation facilitated by a C-terminal translocation signal

Question 13

T6SS

Answer 13

g- only
shares structural features with bacteriophage cell puncturing proteins
consists of intracellular contractile and membrane bound molecular machine
‘poisoned spear’, contact dependent
inter-bacterial combat