What is a ubiquitin protein ligase?
Ubiquitin is a small protein consisting of only 76 amino acids. It is attached to other proteins by an enzyme called a protein ubiquitin ligase in a process known as ubiquitination. Ubiquitin acts as a marker that targets proteins for proteolysis (meaning cleavage of proteins by proteases, enzymes that degrade protein molecules). Ubiquitin is appropriately named since it is ubiquitious and present in essentially all cell types. The process of ubiquitination occurs in three steps: • Ubiquitin is activated by an E1 ubiquitin-activating enzyme. • Activated ubiquitin is transferred from E1 to the ubiquitin-conjugating enzyme E2. • The E3 ubiquitin-ligating enzyme interacts with both the E2 enzyme and the substrate (meaning the molecule upon which an enzyme acts), and transfers ubiquitin to the substrate protein. • Frequently, the process is repeated to form a polyubiquitin chain.
