We discussed that ubiquitin is used to mark proteins for destruction. The covale

Question

We discussed that ubiquitin is used to mark proteins for destruction. The covalent attachment of ubiquitin is carried out by a series of enzymes called E1, E2 and E3 (see Figure below).

The number of each type of enzyme in the eukaryotic genome differs, but generally the number of E1<E2<E3. here’s an example from the simple eukaryote yeast:

E1 enzymes per genome: 1

E2 enzymes per genome: 5

E3 enzymes per genome: 20

Why do you think cells have multiple E2 and E3 enzymes? What’s the advantage?

Explanation / Answer

Ubiquitin protein is subjected to enzymatic post-translational modification, in which protein is attached to a substrate protein. This process is called Ubiquitination. This process most commonly binds the last amino acid of ubiquitin, glycine to a lysine residue on the substrate. Ubiquitination requires 3 types of enzymes.

E1 can bind with many E2s, which can bind with hundreds of E3s in a hierarchical way in the ubiquitination cascade. Having levels within the cascade allows tight regulation of the ubiquitination machinery. Other ubiquitin-like proteins (UBLs) are also modified via the E1–E2–E3 cascade, although variations in these systems do exist.

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