V. Protein Processing, Secretion, and Targeting Flashcards
(30 cards)
What is a chaperone protein?
Chaperone proteins assist in the proper folding and assembly of other proteins.
What are six functions of chaperone proteins?
- Assisting in protein folding
- Preventing aggregation
- Refolding misfolded proteins
- Transporting proteins across membranes
- Stabilizing unfolded proteins
- Assisting in the assembly of multi-protein complexes.
What are four key chaperone proteins found in E. coli?
- DnaK
- GroEL
- GroES
- Trigger factor.
What is the major purpose or function of heat shock proteins?
Heat shock proteins help protect cells from stress by assisting in protein folding and preventing aggregation.
What is the major purpose or function of cold shock proteins?
Cold shock proteins help stabilize RNA and proteins under low-temperature conditions.
What are translocases?
Translocases are protein complexes that facilitate the transport of proteins across membranes.
What are two major functions of the Sec translocase system? What energy source is used?
- Transporting unfolded proteins across the membrane
- Inserting membrane proteins.
Uses ATP as the energy source.
What is the major function of the Tat translocase system? What energy source is used?
The Tat translocase system transports folded proteins across the membrane.
Uses the proton motive force as the energy source.
What is a signal sequence and where, on the protein to be transported, is this signal sequence located?
A signal sequence is a short peptide that directs the transport of a protein; it is located at the N-terminus of the protein.
What are two functions of a signal sequence?
- Directing proteins to the correct cellular compartment
- Initiating the transport process across membranes.
How does the function of the SecA protein differ from the function of the SRP?
SecA is involved in the translocation of proteins across the membrane, while SRP (Signal Recognition Particle) directs ribosomes to the membrane for co-translational translocation.
What does ‘Tat’ stand for?
‘Tat’ stands for Twin-arginine translocation.
What is the function of the TatBC protein? What is the function of the TatA protein?
TatBC binds to the substrate and facilitates its transport, while TatA forms a channel through which the substrate is translocated.
How are signal sequences removed from the transported proteins?
Signal sequences are typically cleaved off by signal peptidases after the protein is translocated.
Why are the type I – VI secretion systems needed? (2 reasons)
- To transport proteins outside the cell
- To deliver effector proteins into host cells.
How are the type I – VI secretion systems in gram positive Bacteria and Archaea different from those in gram negative Bacteria?
Gram positive bacteria and Archaea often use different mechanisms and components for secretion compared to gram negative bacteria, which have an outer membrane.
What are six functions of the type I – VI secretion systems?
- Protein secretion
- Delivery of toxins
- Modulation of host immune responses
- Biofilm formation
- Nutrient acquisition
- Cell-cell communication.
What is a translocase channel?
A translocase channel is a protein structure that forms a pore in the membrane through which proteins are transported.
Why are type II and type V secretion systems called ‘two-step’ translocases?
They are called ‘two-step’ translocases because they involve two distinct phases: translocation across the inner membrane and then across the outer membrane.
What are examples of proteins secreted by type II translocases?
Examples include enzymes and toxins that are secreted into the extracellular environment.
Why are type V secretion systems called ‘autotransporters?’
They are called ‘autotransporters’ because the protein itself facilitates its own transport across the membrane.
Why do type V secretion systems require chaperone proteins?
Type V secretion systems require chaperone proteins to assist in the proper folding of the autotransporter before transport.
What are examples of proteins secreted by type V translocases?
Examples include adhesins and virulence factors.
Why are types I, III, IV, and VI secretion systems called ‘one-step’ translocases?
They are called ‘one-step’ translocases because they transport proteins directly from the cytoplasm to the extracellular space or into host cells without a periplasmic intermediate.
