Chapter 6: Molecular Information flow and protein processing

Microbiology, Exam 2 Review (Slide 65-92)

Where can exported proteins be directed within or outside a cell?

Periplasm, cytoplasmic membrane, outer membrane, or the extracellular environment

What energy sources are typically required for protein secretion systems?

ATP, GTP, or proton motive force

What is the function of Halomucin in Haloquadratum walsbyi?

It is a secreted protein that protects the organism from desiccation

What is the primary function of translocases?

To transport proteins into or through bacterial and archaeal membrane

What is the key difference between the Sec and Tat translocase pathways?

Sec exports unfolded proteins and inserts integral membrane proteins; Tat transports fully folded proteins

Where is the signal sequence located on a protein targeted for transport?

At the N-terminus

What is the typical size and composition of a protein signal sequence?

15–20 residues, usually starting with positively charged amino acids, followed by hydrophobic residues, and ending with polar residues

What are the two major roles of a signal sequence during protein export?

It signals export to the translocase and prevents the protein from completely folding before export

In the Sec system, what molecule recognizes unfolded proteins destined for the periplasm?

SecA

In the Sec system, what molecule recognizes proteins destined to be inserted into the membrane?

Signal Recognition Particle (SRP)

What energy source drives protein translocation via SecA?

ATP

How does the Signal Recognition Particle (SRP) function to deliver membrane proteins?

It binds through co-translation, moving the ribosome directly to the membrane surface

What does "Tat" stand for in the Tat secretion system?

Twin-arginine translocase

What specific types of proteins are processed by the Tat system?

Cofactor-containing proteins (e.g. iron-sulfur proteins, cytochromes, and respiratory enzymes)

What unique sequence motif is required for substrate recognition by the Tat system?

A short signal sequence containing two consecutive arginine residues

Which components of the Tat system recognize the signal sequence and which component serves as the transporter?

TatBC recognizes the signal sequence; TatA forms the membrane transporter channel

What are the specialized proteins inserted or secreted by Gram-negative secretion systems called?

Effectors

Which Gram-negative secretion systems are classified as two-step translocases?

Types II and V (they depend on Sec or Tat to cross the inner membrane first)

What is the path of a protein secreted via the Type II secretion system?

It travels from the periplasm to the environment through a system-specific outer membrane pore

Why is the Type V secretion system often referred to as an "autotransporter"?

The protein to be secreted is physically fused to its own transmembrane domain which forms the outer membrane pore.

Which Gram-negative secretion systems are classified as one-step translocases?

Types I, III, IV, and VI

What are the three core structural components of a Type I secretion system?

A cytoplasmic membrane transporter, an outer membrane pore, and a membrane fusion protein

What is the primary pathogenic function of the Type III secretion system (T3SS)?

It injects toxins (effectors) directly into eukaryotic host cells

What are two common descriptive nicknames for the Type III secretion system machinery?

Injectisomes" or "Needle and Syringe"

To what structural cellular component is the Type III secretion system evolutionarily related?

Bacterial flagella

What is the most common physiological role of the Type IV secretion system (T4SS)?

Transferring DNA through bacterial conjugation (though it can also take up/release DNA and translocate effectors)

What structural entity is the Type VI secretion system (T6SS) action closely related to?

Bacteriophage tails (acting as a cytoplasmic injector into host or rival bacterial cells)