The post-translational attachment of ubiquitin (IPR000626) to proteins (ubiquitinylation) alters the function, location or trafficking of a protein, or targets it to the 26S proteasome for degradation [1, 2, 3]. Ubiquitinylation is an ATP-dependent process that involves the action of at least three enzymes: a ubiquitin-activating enzyme (E1), a ubiquitin-conjugating enzyme (E2, IPR000608), and a ubiquitin ligase (E3, IPR000569, IPR003613), which work sequentially in a cascade [4]. The E1 enzyme is responsible for activating ubiquitin, the first step in ubiquitinylation. The E1 enzyme hydrolyses ATP and adenylates the C-terminal glycine residue of ubiquitin, and then links this residue to the active site cysteine of E1, yielding a ubiquitin-thioester and free AMP. To be fully active, E1 must non-covalently bind to and adenylate a second ubiquitin molecule. The E1 enzyme can then transfer the thioester-linked ubiquitin molecule to a cysteine residue on the ubiquitin-conjugating enzyme, E2, in an ATP-dependent reaction.

This entry also contains the SUMO activating enzyme E1.

1. Polyubiquitin chains: polymeric protein signals. Curr. Opin. Cell Biol. 8, 610-6
2. The ubiquitin-mediated protein degradation pathway in cancer: therapeutic implications. Eur. J. Cancer 40, 2217-29
3. The novel functions of ubiquitination in signaling. null 16, 119-26
4. Getting into position: the catalytic mechanisms of protein ubiquitylation. Biochem. J. 379, 513-25

The post-translational attachment of ubiquitin (IPR000626<
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