The Marking of a Protein by Polyubiquitylation to Signify Degradation

Question

The marking of a protein by polyubiquitylation to signify degradation …
A) requires the hydrolysis of one ATP molecule to ADP per polyubiquitin chain.
B) involves covalent attachment of the target protein to the E1 enzyme.
C) is carried out by the proteasome complex.
D) is typically done on an arginine residue in the target protein.
E) involves the recognition of the target protein by an E2-E3 ligase.

Accepted Answer

In this pathway, each ubiquitin molecule is activated by linkage to an E1 enzyme via a thioester bond, at the expense of two ATP equivalents. The ubiquitin is then transferred onto an E2 enzyme that is part of an E2-E3 ubiquitin ligase complex. The latter recognizes the target protein and transfers the ubiquitin to a lysine residue in the target protein or to Lys48 of the previous ubiquitin in the chain. A protein marked with this polyubiquitin chain is then recognized and degraded by the proteasome.