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MICRO > Prokaryotic Protein Secretion Systems > Flashcards

Prokaryotic Protein Secretion Systems Flashcards

1
Q

True or false, not all protein secretion systems require energy

A

False, they all do

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2
Q

What is placed onto most proteins needed to be secreted by the cell?

A

N-terminus signal peptides

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3
Q

What does each signal peptidase do?

A

SP1 - cleaves off the signal peptide of almost all proteins

SP2 - cleaves off the signal peptide of Lipo Proteins

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4
Q

Are signal peptides conserved molecules?

A

No, but there are three conserved area’s.

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5
Q

Explain the three conserved area’s of signal peptides

A

1) (+) N region terminus (n region)
2) hydrophobic core (h region)
3) (-) C Terminus which is also hydrophilic (c region)

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6
Q

Explain Lipoprotein signal peptides

A
  • also have c, n , h region
  • has a LIPO box region which contains a positive cysteine group
  • this cysteine group must be lipid modified before the SP is cleaved
  • is monitored by SP 2
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7
Q

where are signal peptides cleaved in lipoproteins?

A

just before the fatty acid cysteine that is apart of the LIPO box

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8
Q

Explain the SEC dependent pathway

A
  • proteins needed to be secreted are made as precursor proteins with a N - terminal signal peptide
  • signal peptides delay the folding of the protein
  • chaperone proteins maintain the unfolded precursor
  • Translocon in PM transfers the protein through the PM and uses SP 1 or 2 to cleave signal peptide
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9
Q

What is the GSP?

A

General secretion pathway. This is the same thing as SEC dependent pathway

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10
Q

How far can the GSP get a protein?

A

only through the PM and into the periplasm

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11
Q

What is the SEC system?

A

The system to get a protein into the periplasm

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12
Q

What is SecB?

A

the cytoplasmic chaperone protein that keeps the precursor protein unfolded and stable

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13
Q

What is SecA?

A

just an ATPase that provides energy for export

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14
Q

What proteins form the channel complex to secrete the new protein?

A

Sec Y, E, G

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15
Q

What is Post-translational secretion?

A

Entire protein is synthesized before translocation. E.g the Brauns lipo protein in gram negative cells

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16
Q

What is Co-translational secretion?

A

synthesis occurs at the same time as secretion

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17
Q

What part of the protein enters the Sec pathway first?

A

the N terminus in most pathways. This is because the signal peptide is located on it. If the signal peptide was some how on the C - terminus then Co-translational secretion is impossible.

18
Q

What is the high affinity SecA binding site?

A

Sec Y and Sec E of the channel

19
Q

Explain what the type 2 secretion system achieves and what it secretes?

A
  • type 2 secretion gets proteins past the periplasm and through the Outer Membrane
  • uses SEC SYSTEM to get proteins into periplasm therefore sec dependent
  • many pathogens use Type 2 to secrete toxins, proteases, and lipase’s
20
Q

Most of the the Type 2 secretion proteins are OMP’s. T or F

A

false, most are PM integral proteins

21
Q

What is the only component in the OM for type 2 secretion?

A

Secretin

22
Q

How does the type 2 secretion system get proteins out of OM (3)

A
  • secretin forms pore in OM
  • Several integral proteins form and miniature type IV pilus called a piston
  • addition of subunits and extraction of subunits extends and pulls back piston to shove out protein through Secretin
23
Q

what are pseudopilins?

A

integral proteins homologous to type IV pili. There are 5 involved in type 2 secretion. These form the actual piston

24
Q

Explain what Type 1 secretion system achieves? (3)

A
  • exports proteins as a complete protein through both the PM and OM
  • therefore SEC INDEPENDENT
  • proteins have signal on C terminus therefore this is always post-translational secretion
25
Q

What is ABC / ATP binding cassette secretion?

A

same thing as TYPE 1 secretion

26
Q

True or false, the C terminus signal in type 1 secretion is never cleaved off

A

True, unlike signal peptides on N - terminus

27
Q

What are the three components of type 1 secretion pathways?

A
  • ATP cassette binding protein
  • MFP (membrane fusion protein)
  • OMP
28
Q

what does the cassette binding protein do? what is its composition?

A
  • type 1
    It is comprised of NBD (nucleotide binding domain) and is fused to the PM.
  • IT IS RESPONSIBLE FOR PROTEIN SPECIFICITY and provides energy
29
Q

what does the MFP do?

A
  • type 1
    Short cytoplasmic domain and large N terminal periplasmic domain
    upon ATP cassette protein binding, it connect the OM with the PM allowing a protein to skip the periplasm.
30
Q

What does the OMP do?

A
  • is generated upon initial interaction of ABC protein and substrate
  • forms water filled pore for protein to leave through
31
Q

What protein discovered the type 1 secretion system?

A

Hemolysin of E. coli

32
Q

explain the 3 components of the hemolysin type 1 secretion pathway

A

HylB - ABC protein
HlyD - MFP
TolC - OMP compartment

hemolysin is coined HlymA and has a 50AA C terminal signal

33
Q

What secretion system makes proteins go from cytoplasm directly to another cytoplasm? What is normally transported like this?

A
  • (TTSS) Type 3 secretion is sec independent and has no periplasm intermediate!!
  • normally pathogen virulence proteins are translocated like this
34
Q

how does TTSS accomplish its translocation of proteins?

A

Uses a needle complex NC with structural similarities to the basal body of flagella. Roughly 70 nm long

35
Q

Explain the needle complex in type 3 secretion. How many proteins involved?

A
  • 30 proteins 8 being homologous to basal body of flagella
  • At the tip of the needle is a a complex that forms a pore in prey cells
  • proteins pass through the needle in a semi unfolded state because the pore is so thin
36
Q

How does the cell know a protein is going through TTSS?

A
  • the N - terminus does not have a signal peptide, but it must have at least 12 N-terminal amino acids.
  • middle residues of roughly 50-150AA’s are chaperone binding and targeting to TTSS
  • the rest of the AA’s have effector activity often altering transduction pathways in the host
37
Q

What is conjugation?

A

Transfer of genetic info from one bacteria to another via direct contact.

38
Q

explain type 4 secretion system purpose

A

it secretes proteins and transfers DNA vi conjugation. It is sec independent

39
Q

explain the purpose of type 5 secretion system

A
  • proteins that go through this system are called autotransporters
  • they are SEC Dependent pathways
  • protein has 3 domains
40
Q

Explain the 3 domains of autotransporters

A

N terminal domain contains signal peptide
middle domain contains effector region
Conserved C terminal domain which is able to form its own pore in the OM

MICRO (28 decks)

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