E1 Activating Enzymes 12 Products

To date eight E1 enzymes have been identified, two characterized from the human genome comprise three domains; an adenylation domain which binds ATP and ubiquitin, a catalytic cysteine domain (CCD) which binds activated ubiquitin, and a C-terminal ubiquitin-fold domain (Ufd) which recruits specific E2 conjugating enzymes. E1 enzymes utilise ATP to activate the terminal glycine residue of ubiquitin/UBL generating a covalent thioester linkage between ‘activated’ ubiquitin/UBL and the E1 enzyme itself. Ubiquitin/UBL is then transferred to the sulphydryl group of the active-site cysteine on an E2 conjugating enzyme in a transthiolation reaction.