Ubiquitinylation

Question 1

In what life stage of a protein are the HSP70 and HSP60 proteins involved?

Answer 1

HSP70 is involved in the early life of a protein
HSP60 is involved in fully synthesized proteins

Question 2

What are all the components of a proteasome and what are their functions?

Answer 2

The Cap has ubiquitin receptor for recognition of tagged protein (with ubiquitin). Ubiquitin hydrolase to detach and recycle ubiquitin. Unfoldase-activity will unfold the protein. Protein is led into central cylinder where it is cleaved by protease from protein into amino acids.

Question 3

Why are there many types of E3 ligases?

Answer 3

E3 ligases are primarily responsible for the specific recognition of a large number of proteins, this requires specificity and versatility. This requires many different ones.

Question 4

Give 2 examples of E3 ligase families and describe their mechanism of action. Draw a scheme to explain your answer.

Answer 4

E3 ligases are used for ligation of Ub bound to E2 to the substrate.
HECT E3: Binds both E2 with the attached Ub and the substrate. Ub is first transferred to HECT E3 and then to the substrate
RING E3: also binds both E2 with attached Ub and the substrate. Brings substrate and E2 in close proximity. Ub is directly transferred to the substrate. (not via the E3 itself).

Question 5

Describe how chaperones aid to correct folding of proteins and what happens with incorrectly folded proteins.

Answer 5

Chaperones recognize hydrophobic parts of proteins. These are normally not exposed but buried inside. When exposed after incorrect folding, chaperones recognize this and aid in correct folding.

Incorrectly folded proteins are digested by the proteasome