Lecture 13

Question 1

Where are proteins made?

Answer 1

cytoplasm

Question 2

What is protein secretion?

Answer 2

The translocation of proteins from the cytoplasm to any other compartment

Question 3

How do proteins know where to go?

Answer 3

They have signal sequences at the N-terminal

Question 4

How do proteins get into the inner membrane?

Answer 4

Some have hydrophobic tails or loops and don’t need assistance. Other have a signal recognition particle (SRP) and a small RNA molecule ffs will escort the protein to the secretory proteins in the membrane.

Question 5

What is the Sec system?

Answer 5

help proteins journey beyond the cell membrane

Question 6

What does SecA do?

Answer 6

SecA recognizes signal sequence (why N-terminal?) as it comes out of the ribosome and brings it to the SecYEG channel

Question 7

What does chaperone SecB do?

Answer 7

chaperone SecB helps to make sure the protein doesn’t fold before being translocated

Question 8

What is SecEY channel?

Answer 8

peptide is threaded through the SecEY channel, and the signal peptide is cleaved

Question 9

What is chaperone Skp?

Answer 9

In gram negative to reach the outer membrane, While being translocated by Sec the protein is bound by the chaperone Skp in the periplasm
Prevents degradation by DegP protease
Skp escorts the protein to the Bam complex in the outer membrane

Question 10

What is the Bam complex?

Answer 10

In gram negative to reach the outer membrane, the Bam complex in folding the protein and inserting it into the outer membrane

Question 11

What are the 2 types of mechanisms that bacteria export proteins out of the cell?

Answer 11

Type I: ABC exporter is Sec independent
Type II: Two-step system is Sec dependent

Question 12

How does Type I: ABC exporter is Sec independent work?

Answer 12

1) 3 proteins mediate transport one of which is the ATPase binding cassette (ABC)
2) Operates on proteins lacking a signal sequence
3) Protein exported directly from cytosol into extracellular space
bypasses the periplasm

Question 13

How does Type II: Two-step system is Sec dependent work?

Answer 13

Step 1: Proteins move from cytoplasm to periplasm by Sec system

Step 2: 14 accessory proteins move it from the periplasm across the outer membrane into the extracellular space

Question 14

What is the type III secretion system?

Answer 14

1) T3SSs are double-membrane-embedded nanomachines found in various pathogenic Gram-negative bacteria.

2) Promote the transfer of bacterial effector proteins to the cytoplasm or the plasma membrane of target eukaryotic cells

3) These effectors modulate or subvert specific host cell functions, thereby promoting bacterial invasion and colonization

Question 15

What is the structure of a T3SS injectisome?

Answer 15

This syringe-like structure is composed of approximately 25 proteins organized into 2 main substructures:

a double-membrane-spanning base composed of stacked rings

a needle-like filament that protrudes from the bacterial surface into the extracellular space

—-contact dependent with a host cell

Question 16

How are proteins transported through T3SS?

Answer 16

proteins must be completely unfolded to pass through

Question 17

What did the T3SS evolve from?

Answer 17

flagellum

Question 18

How do type IV secretion systems work?

Answer 18

can translocate DNA and proteins, found in both gram+/-, homology to pili, mediate conjugation of plasma DNA

Question 19

What system does agrobacterium use to create crown gall disease?

Answer 19

type IV

Question 20

Type VI have 2 main roles in what? in what type of cells?

Answer 20

1) pathogenesis
2) bacterial competition

in both eukaryotic and prokaryotic cells

Question 21

What is the composition of type VI secretion systems?

Answer 21

2 main complexes: a membrane complex made of IM proteins that are homologous to components of the T4SS, and a tail complexanchored to the cell envelope by the membrane complex

Tail sheath is a long tubular structure that is perpendicular to the membrane, and extends into the bacterial cell cytoplasm

Question 22

T6SS evolved from what and how do they work?

Answer 22

evolved from phage tails,
Following an extracellular signal, a conformational change in the baseplate complex triggers contraction of the sheath, which translocates the inner tube out of the cell and across a target membrane

Before contraction, effectors are recruited to the spike–tube complex and bind

A single T6SS contraction event shoots multiple effectors/toxins into a target cell

Question 23

What is type V secretion also known as? what is it depended on?

Answer 23

T5SS, also known autotransport, is dependent on the Sec system to get into the periplasm

Question 24

How do type V secretion systems work?

Answer 24

T5SSs are composed of a secreted domain, called the ‘passenger’ domain that is unfolded in the periplasm, and a transmembrane domain called the ‘translocator’ domain

The translocator domain inserts into the OM as a β‑barrel, enabling the secretion of the passenger domain through the pore of the β‑barrel.

Does not require an ATP gradient or a proton gradient: energy for transport derived from the folding of the passenger domain

Question 25

Where are type VII secretion systems found?

Answer 25

T7SS is a specialized secretion apparatus required for the virulence of mycobacteria, such as Mycobacterium tuberculosis.

T7SS gene clusters have also been identified in Gram-positive bacteria

Question 26

In Mycobacterium tuberculosis Type VII Secretion System what is the core channel?

Answer 26

made of membrane proteins EccBCDE

Question 27

What form the central channel in the IM in Mycobacterium tuberculosis Type VII Secretion System?

Answer 27

EccD

Question 28

What does EccC do in Mycobacterium tuberculosis Type VII Secretion System?

Answer 28

functions as a coupling component w/cytoplasmic ATPase

Question 29

What does mycP do in Mycobacterium tuberculosis Type VII Secretion System?

Answer 29

is a membrane preotease involved in substrate processing

Question 30

What 2 cytoplasmic accessory proteins facilitate secretion in Mycobacterium tuberculosis Type VII Secretion System?

Answer 30

ExxA and EspG