Secretion Systems

Question 1

Why would bacteria need secretion systems?

Answer 1

• respond to its environment
• physiological processes
• none are constitutively active

Question 2

Role of the Sec pathway in Gram + and archae

Answer 2

• translocation of proteins across the single plasma membrane

Question 3

Role of the sec pathway in Gram -

Answer 3

• export of proteins into periplasm

Question 4

How does Sec pathway work?

Answer 4

• 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

Question 5

What does Tat stand for?

Answer 5

Twin-arginine transport

Question 6

How does Tat pathway work?

Answer 6

• 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

Question 7

Sec-dependent secretion types

Answer 7

• Type V

- Type II

Question 8

Sec-independent secretion types

Answer 8

• Type IV
• Type III
• Type I

Question 9

Where are Type II systems found?

Answer 9

• only in Gram -ves

Question 10

Main component of Type II systems

Answer 10

• translocation pore in OM

- 12-15 secretin subunits (large enough to accomodate folded protiens

Question 11

4 components of Type II systems

Answer 11

• OM complex
• periplasmic pseudopilus
• IM platform
• cytoplasmic ATPase

Question 12

Bacteria that use Type II system

Answer 12

• P. aeruginosa

- K. pneumoniae

Question 13

What is the Type II IM platform made up of?

Answer 13

4 membrane proteins

- GspC, F,L,M

Question 14

What makes the Type V system unique?

Answer 14

• substrate and secretion pore fuse to form a single polypeptide

Question 15

2 domains of Type V autotransporters

Answer 15

• N-terminal passenger domain

- Conserved C-terminal domain (forms a transmembrane B-barrel pore)

Question 16

Bacteria that use Type V system

Answer 16

• N. gonorrhoeae

- N. meningitides

Question 17

Characteristics of Type I system

Answer 17

• 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

Question 18

Describe Type 1 system channel

Answer 18

Tripartite double-membrane spanning channel

• ATP-binding cassette transporters (ABCs)
• Outer membrane protein (OMP)
• membrane fusion proteins (MFPs)

Question 19

2 groups of ABC transporters in Type I system

Answer 19

• for large proteins from Gram -ves

- for small protiens and peptides

Question 20

Components of Type I system

Answer 20

• TolC
• HlyD (MFP)
• HlyB (ABC)

Question 21

Main component of Type III system

Answer 21

• 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

Question 22

How is the Type IV system unique?

Answer 22

• can transport nucleic acids as well as proteins directly into host cells

Question 23

Most common role of Type IV sytem

Answer 23

• to mediate conjugation of plasmid DNA

Question 24

Examples of bacteria that use Type IV system

Answer 24

• H. pylori
• Rickettsia
• B. pertussis

Question 25

Machinery of Type VI

Answer 25

2 main complexes

• membrane complex
• tail complex

Question 26

Example of bacteria that use Type VI

Answer 26

• V. cholerae

- P. aeruginosa