Toxins and secretion systems 3 Flashcards
Different types of protein secretion in dierms?
Some take it directly from the donor cells cytoplasm to the recipients cytoplasm
Some just take it to the external environment
Non-periplasmic intermediate diderm secretion?
From bacterial cytoplasm to extracellular milieu in one step
Nano-machine spanning both membranes and periplasm
Periplasmic intermediate diderm secretion?
First step: translocation across CM:
Second step: Translocated across OM
What is the SEC pathway?
Protein secretion pathway found in all domains of life
Takes proteins across or inserts them into the cytoplasmic membrane
How are proteins targeted for secretion via the sec pathway translocated?
In an unfolded or partially folded state
What is the TAT pathway?
Twin Arginine Translocation, found in bacteria and some archaea
How are proteins targeted for secretion via the TAT pathway translocated?
Proteins are fully folded
They contain a conserved twin-arginine motif in their signal peptide
What are secretion systems?
Specialised machinery in bacteria that transport proteins out of the cell
Can move proteins aros the cytoplasmic and sometimes the outer membrane
Two ways the SEC pathway can transport proteins?
SRP and SecA pathways
Why does the SEC pathway transport unfolded proteins?
The tunnels that the SEC pathway uses are too narrow for folded proteins to pass through
Difference between SRP and secA pathways?
SRP is shorter, non-matured proteins directly from the ribosome while the Seca pathway has matured a little, is longer and isnt directly from the ribosome
WHat regions does the sec signal have?
n region, h region, c region
How are proteins targeted to the SEC or TAT pathway?
Nucleotide sequences that are recognised by the ribosome–> co-translational targeting
Protein components of the SEC pathway?
SecTEG trimer, Sec A-ATPase, LepB-peptidase
What does the SecYEG trimer do in the SEC pathway?
Forms a channel in the membrane
What does the Sec A-ATPase do in the SEC pathway?
binds to SecYEG
What does the Lep B-peptidase do in the SEC pathway?
Cleaves the signal peptide
What does SecB do in the SEC pathway?
Transports the protein from the ribosome to the SecA
WHat provides the energy for the SEC pathway?
ATP
What provides the energy for the TAT pathway?
Proton motive force
First step of TAT pathway?
Signal peptide on the cargo is recognised by the TATABC, and binds to TATC
What happens after the signal peptide motif binds to the TATC?
The signal bends –> conformational changes
Bends and dimerises bc of hairpin reigon
What happens when the signal peptide is undergoing a conformational change?
The B subunit of TATABC displaces, and the A subunit makes a tunnel
How many secretion systems are there?
9
