Ubiquitin is activated in an ATP-dependent manner, catalyzed by E1 ubiquitin-activating enzymes. In the first step of ubiquitin activation, the E1 enzyme binds ATP, Mg+2 and ubiquitin, and catalyses ubiquitin C-terminal acyl-adenylation (Ubiquitin-AMP). In the second step, the catalytic cystine in the E1 attacks the ubiquitin-adenylate (Ub-AMP) to form the activated ubiquitin-E1 thioester-bonded complex and an AMP leaving group. The intermediate reaction involving the formation of the ubiquitin-AMP complex is not represented here.
Bohnsack, RN, Tokgöz, Z, Haas, AL
Schulman, BA, Harper, JW
Schindelin, H, Lee, I
ubiquitin-protein transferase activity of Ubiquitin activating E1 enzymes [cytosol]
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