Protein Sorting

Question 1

Cytoplasmic pathway protein destinations.

Answer 1

Cytosol, mitochondria, nucleus, peroxisomes.

• Protein synthesis begins and ends on free ribosomes in cytoplasm.

Question 2

Secretory Pathway protein destinations.

Answer 2

ER, lysosomes, plasma membrane, secretion out of cell.

• Translation begins on free ribosomes but terminates on ribosomes sent to ER.

Question 3

Cytosolic destined proteins sorting signal.

Answer 3

None.

Question 4

Mitochondrial destined proteins sorting signal.

Answer 4

N-terminal hydrophobic alpha helix. Interacts with chaperone protein (HSP70). Passes through TOM/TIM.

Question 5

Nuclear destined protein sorting signal.

Answer 5

Basic residues - KKKRK

Lysine and Arginine

Question 6

Peroxisomal destined protein sorting signal.

Answer 6

C-terminal SKL

Serine, Lysine, Leucine.

Question 7

ER lumen destined protein sorting signal.

Answer 7

KDEL

Lysine, Aspartic Acid, Glutamic Acid, Leucine

Question 8

Lysosomal destined protein sorting signal.

Answer 8

Mannose-6-phosphate

Question 9

Membrane destined protein sorting signal.

Answer 9

N-terminal apolar region.

Question 10

Secretory destined protein sorting signal.

Answer 10

Tryptophan domain.

Question 11

ER-targeting signal peptide for each protein in the secretory pathway.

SRP mechanism with ER membrane.

Answer 11

15-60 A.A. at N-terminus of protein.

• 1 or 2 basic amino acids (Lys or Arg) near N-terminus.
• An extremely hydrophobic sequence (10-15?residues) on C-terminus of the basic residues.

Signal Recognition Particle (SRP) binds ribosomal complex to pause translation. SRP-bound ribosome binds to SRP receptor on ER membrane. Translation continues and polypeptide is translocated into the ER.