Protein Sorting Flashcards
What is the defect that causes cystic fibrosis?
ER exit in CFTR (deltaF508) or golgi exit in CFTR (C-terminal PDZ)
Protein is transported to the mitochonrdion (matrix)
1) Location of Sequence within protein
2) Removal of Sequence?
3) Nature of Sequence
1) N-terminus
2) Yes
3) Amphipathic helix, 20-50 residues in length, with Arg and Lys residues on one side and hydrophobic residues on the other
Protein is transported to the Endoplasmic reticulum (lumen)
1) Location of Sequence within protein
2) Removal of Sequence?
3) Nature of Sequence
1) N-terminus
2) Yes
3) Core of 6-12 hydrophobic amino acids, often preserved by one or more basic amino acids (Arg, Lys)
Protein is transported to the Peroxisome (matrix)
1) Location of Sequence within protein
2) Removal of Sequence?
3) Nature of Sequence
1) C-terminus (most proteins)
N-terminus (few proteins)
2) No
3) PTS1 signal (Serine, Lysine, Leucine) at extreme C-terminus; PTS2 signal at N-terminus (SKL motif)
Protein is transported to the Nucleus (nucleoplasm)
1) Location of Sequence within protein
2) Removal of Sequence?
3) Nature of Sequence
1) Varies
2) No
3) Multiple different kinds; a common motif includes a short segment rich in Lysine and Arginine residues
Uptake of precursor proteins into mitochondria can be assayed in a ____.
cell-free system
Uptake of precursor proteins into mitochondria requires ____.
proton-motive force, ATP, and cytosolic chaperones
What are the energy inputs for protein import into the mitochondrial matrix?
Hsc70 ATPase outside, Hsc70 ATPase inside, proton-motive force across IMM
Signal peptide for import into the mitochondrial matrix
Signal peptide is an N-terminal, amphipathic alpha-helix; 20-50 residues long, with R and K on one side and delta on the other
Hsc70 in the cytosol keeps protein unfolded
Translocation is post-translational
Name a chaperone protein
Hsp70
Co-chaperone accessory proteins
DnaJ and Hsp40; GrpE and BAG1
DnaJ and Hsp40 stimulate the hydrolysis of ATP to ADP
GrpE and BAG1 converts the Hsp70 back to the open form
Tom20/22
Import receptor; outer mitochondrial membrane complex that recognizes N-terminal mtSP (mitochondrial signaling peptide)
Import receptor on the mitochondrial membrane
Tom20/22
Tom40
Import pore (on the outer mitochondrial membrane that associates with Tom20/22); part of the translocon (transport proteins into the mitochondrial matrix)
The translocon (of mitochondria) is ____.
Tom40 and Tim23/27
Tim23/27
located on the inner mitochondrial membrane, part of the translocon (transports proteins into the mitochondrial matrix)
Steps of import of protein into mitochondrial matrix.
- N-terminus signaling peptide recognized by Tom20/22
- Protein moves across outer membrane through Tom40
- Protein moves across inner mitochondrial membrane through Tim23/17.
- Signal sequence cleaved/removed by matrix protease.
- Matrix Hsc70 binds to the imported polypeptide to facilitate uptake. It is targeted to the translocon through binding Tim44. (Tim 44 is bound to Tim23/17?)
Mitochondrial matrix protein must be translocated in the ____ state.
Unfolded
Pathways for transporting proteins from the cytosol to the inner mitochondrial matrix
Path A: Most like matrix sorting. Uses a matrix targeting sequence and a stop-transfer sequence. (Tom20/22 and Tom40, Tim23/17, and Tim44 and Hsc70)
Path B: Uses a matrix targeting sequence and an Oxa1-targeting sequence (Tom 40, Tim23/27, Hsc70, Oxa1)
Path C: No N-termination targeting sequence. Different receptor (Tom 70), Intermembrane chaperone (Tim9/10). Different IMM translocon (Tim22/54)
function of peroxisomes
oxidation of organic substrates and fatty acids (metabolism of fatty acids)
producing acetyl-CoA
Import of peroxisomal matrix proteins is directed by ____.
PTS1 targeting sequence
C-terminal and contains sequence SKL; not cleaved after import
PTS1 targeting sequence
sequence SKL, c-terminal, not cleaved after import. Pex5 recognizes the sequence.
Import of peroxisomal matrix proteins steps
- Pex5 (cytosolic) recognizes PTS1 targeting sequence (SKL sequence on C-terminus)
- Pex14 (membrane protein) associates with Pex5 and may be the translocon. Pex5 and the protein cross the membrane into the peroxisomal matrix.
- Pex5 and protein disassociate and Pex5 is exported through a Pex2,Pex10, and Pex12 complex.
Folded proteins with ___ are also translocated.
metal cofactors
Sorry about this one. It was on the slide.
