Question

Which AA does ubiquitin bind? Why/How?

A) Lysine; Forms Stable Bonds with Ubiquitin
B) Serine; Induces Ubiquitin Conformational Change
C) Glycine; Initiates Ubiquitin Binding Cascade
D) Arginine; Facilitates Ubiquitin Hydrolysis

Answer 1

Ubiquitin binds to lysine residues on target proteins through the formation of an isopeptide bond, involving a series of enzymatic reactions that culminate in the target protein's recognition and degradation by the proteasome.

Step-by-step explanation:

Ubiquitin binds to the amino acid lysine on the substrate protein. This occurs through the formation of an isopeptide bond between the carboxyl terminus of ubiquitin and the ε-amino group of lysine. Ubiquitination involves a cascade of enzymatic reactions. Initially, ubiquitin is activated by an ubiquitin-activating enzyme (E1), which requires ATP hydrolysis. The activated ubiquitin is then transferred to an ubiquitin-conjugating enzyme (E2). Finally, the ubiquitin ligase enzyme (E3) facilitates the transfer of ubiquitin from the E2 enzyme to a lysine residue on the substrate protein targeted for degradation. Often, a polyubiquitin chain is formed by the addition of multiple ubiquitin molecules to a single lysine within the first ubiquitin or to other lysine residues on subsequent ubiquitins. The polyubiquitinated protein is then recognized by the proteasome for degradation.