A family of enzymes (ubcs), more than 30 in humans, that are involved in the addition of ubiquitin to proteins thereby ‘flagging’ them for degradation. The E1 enzyme (ubiquitin-activating enzyme) adenylates ubiquitin and forms a thioester-linked complex that is transferred to the E2 enzyme which interacts with an E3 ligase that transfers the ubiquitin to the target protein. There are multiple E3 ligases generally subdivided into four classes: HECT-type, RING-type, PHD-type, and U-box containing, each of which targets specific proteins. See also N-end rule.
Subjects: Medicine and Health — Chemistry.