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HECT Domain
Class:Ubiquitin processes

No Image The crystal structure of the HECT domain of E6AP reveals a bilobal structure with a broad catalytic cleft at the junction of the two lobes. The cleft contains conserved residues involved in the formation of the ubiquitin-thioester bond. In the co-crystal structure of E6AP with E2 UbcH7, the E2 binds to a large hydrophobic groove in an approximatley 80 amino acid sub-domain of the N-terminal lobe of the HECT domain. The combined HECT-E2 complex forms a U-shaped structure with the active site cysteine side chains approximately 41 A apart with an open line of sight. The figure shows the HECT domain of E6AP.

Structure Reference:
Huang, L. et al. (1999) Science. 286(5443):1321-1326. PDB: 1C4Z.

Domain binding and function:
 structure The HECT domain, short for Homologous to the E6-AP Carboxyl Terminus, is an approximately 40 kDa (350 amino acid) catalytic domain found at the carboxy-terminus of Hect-class E3 ubiquitin protein ligases. This domain functions to bind specific E2s, accepts ubiquitin from the E2 to form a ubiquitin-thioester intermediate with the HECT active cysteine, and then transfers ubiquitin to either the e-amino groups of lysine side chains of the substrate or to the growing end of multi-ubiquitin chains. The formation of a thioester intermediate with Ub is unique to Hect E3s and has not been observed with other classes of E3s.
Examples of Proteins: 
HECT domain protein
Binding partner
E6AP UbcH7
Nedd4 UbcH5
HectH7 UbcH7
HectH6 (p532) UbcH5

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