Lecture 13 Flashcards
Where are proteins made?
cytoplasm
What is protein secretion?
The translocation of proteins from the cytoplasm to any other compartment
How do proteins know where to go?
They have signal sequences at the N-terminal
How do proteins get into the inner membrane?
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.
What is the Sec system?
help proteins journey beyond the cell membrane
What does SecA do?
SecA recognizes signal sequence (why N-terminal?) as it comes out of the ribosome and brings it to the SecYEG channel
What does chaperone SecB do?
chaperone SecB helps to make sure the protein doesn’t fold before being translocated
What is SecEY channel?
peptide is threaded through the SecEY channel, and the signal peptide is cleaved
What is chaperone Skp?
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
What is the Bam complex?
In gram negative to reach the outer membrane, the Bam complex in folding the protein and inserting it into the outer membrane
What are the 2 types of mechanisms that bacteria export proteins out of the cell?
Type I: ABC exporter is Sec independent
Type II: Two-step system is Sec dependent
How does Type I: ABC exporter is Sec independent work?
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
How does Type II: Two-step system is Sec dependent work?
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
What is the type III secretion system?
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
What is the structure of a T3SS injectisome?
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
How are proteins transported through T3SS?
proteins must be completely unfolded to pass through
What did the T3SS evolve from?
flagellum
How do type IV secretion systems work?
can translocate DNA and proteins, found in both gram+/-, homology to pili, mediate conjugation of plasma DNA
What system does agrobacterium use to create crown gall disease?
type IV
Type VI have 2 main roles in what? in what type of cells?
1) pathogenesis
2) bacterial competition
in both eukaryotic and prokaryotic cells
What is the composition of type VI secretion systems?
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
T6SS evolved from what and how do they work?
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
What is type V secretion also known as? what is it depended on?
T5SS, also known autotransport, is dependent on the Sec system to get into the periplasm
How do type V secretion systems work?
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
Where are type VII secretion systems found?
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
In Mycobacterium tuberculosis Type VII Secretion System what is the core channel?
made of membrane proteins EccBCDE
What form the central channel in the IM in Mycobacterium tuberculosis Type VII Secretion System?
EccD
What does EccC do in Mycobacterium tuberculosis Type VII Secretion System?
functions as a coupling component w/cytoplasmic ATPase
What does mycP do in Mycobacterium tuberculosis Type VII Secretion System?
is a membrane preotease involved in substrate processing
What 2 cytoplasmic accessory proteins facilitate secretion in Mycobacterium tuberculosis Type VII Secretion System?
ExxA and EspG
