Question

Which of the following proteins determines which protein lives or dies by ubiquitin-mediated degradation?

1) HSP-70
2) Ubiquitin Activating Enzyme
3) E2
4) E3
5) Proteasome core

Answer 1

The E3 ubiquitin ligase determines which protein is marked for ubiquitin-mediated degradation by attaching ubiquitin to it. This ubiquitin tag signals the proteasome to degrade the tagged protein, with E1 and E2 enzymes aiding in this process.The correct option is 4).

Step-by-step explanation:

The protein that determines which protein is targeted for ubiquitin-mediated degradation is the E3 ubiquitin ligase. In the process of tagging proteins for degradation, an ubiquitin group is added to a protein, thereby marking it for destruction. This ubiquitination process involves several steps:

Ubiquitin is activated through ATP hydrolysis and binds to an ubiquitin-activating enzyme (E1).

Ubiquitin is transferred to an ubiquitin-conjugating enzyme (E2).

Finally, the ubiquitin ligase (E3) facilitates the transfer of ubiquitin from E2 to the target protein, thereby determining the specificity of protein degradation.

Further ubiquitins are bound to the complex, forming a poly-ubiquitinated protein.

The poly-ubiquitinated protein is then recognized by the proteasome, where it is ultimately degraded into peptide fragments.

The E3 ubiquitin ligase is crucial in this process as it is responsible for the specific recognition of the target protein that needs to be degraded. After tagging by ubiquitins, proteins are unfolded and enter the proteasome core, where they are digested to amino acids.