Pili

Question 1

What does the term pilus/pili refer to?

Answer 1

Hair-like multimeric structures that are peritrichous, rigid and rod like. Tipped with adhesins and found on the surface of bacterial cells

Question 2

There are 4 families of pili in Gram-negative bacteria. What are these?

Answer 2

1. Chaperone-usher pathway: Type 1 pili, P pili, Dr/Afa family
2. Type IV pili: MCP, GCP, BFP, TCP
3. Nucleation precipitation pathway assembled pili: Curli
4. Alternative chaperone usher pathway assembled pili: CS1

Question 3

What do the components of a Type 1 pilus do?

Answer 3

Assembled in the periplasma, uses Sec translocon to transport proteins here from cytosol.
Fim C - chaperone. Stabilises FimA, FimF, FimG and FimH. This prevents aggregation in the periplasma.
FimD - usher. Forms 2-3nm channels, binds FimA-H/C. Facilitates uncapping of FimA
DsbA - Periplasma protein which introduces disulfide bridges to FimA (integrity)

Question 4

What are the components of a Type 1 pilus?

Answer 4

Sec translocon
Fim A, C, D, F, G, H
DsbA

Question 5

How do Type 1 pilins polymerise?

Answer 5

Non-covalently.
Each pilin has a missing beta-strand which is filled in by a chaperone (donor strand complementation) until it is replaced by the N-terminal extension of the next pilin (donor strand exhange)

Question 6

What are the components of a Type IV pilus?

Answer 6

Pil B, C, D, E, G, Q, T

Question 7

What do the components of a Type IV pilus do?

Answer 7

PilB - assembly ATPase
PilC - adhesin ?
PilD - preplin peptidase
PilE - pilin
PilG - ATPase-associated protein
PilQ - secretin, forms a gated channel
PilT - retraction ATPase (opposite of PilB)

Question 8

Where are Type IV pili assembled?

Answer 8

In the inner membrane. Energy is not required for this assembly

Question 9

What is involved in pilus assembly in Gram-positive bacteria?

Answer 9

Sortase C - pilus assembly sortase (enzyme)
Recognises sortase recognition site and cuts between T and G in signal peptide. Makes covalent amide bonds (NH2 side chain of internal lysine of next subunit) between pilins and adhesin. Bonding to an adaptor stops growth of pili.