Transferases;
Acyltransferases;
Aminoacyltransferases
BRITE hierarchy

[E2 ubiquitin-conjugating enzyme]-S-ubiquitinyl-L-cysteine:[acceptor protein] ubiquitin transferase (isopeptide bond-forming)

[E2 ubiquitin-conjugating enzyme]-S-ubiquitinyl-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-N6-ubiquitinyl-L-lysine (overall reaction);
(1a) [E2 ubiquitin-conjugating enzyme]-S-ubiquitinyl-L-cysteine + [HECT-type E3 ubiquitin transferase]-L-cysteine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + [HECT-type E3 ubiquitin transferase]-S-ubiquitinyl-L-cysteine;
(1b) [HECT-type E3 ubiquitin transferase]-S-ubiquitinyl-L-cysteine + [acceptor protein]-L-lysine = [HECT-type E3 ubiquitin transferase]-L-cysteine + [acceptor protein]-N6-ubiquitinyl-L-lysine

[E2 ubiquitin-conjugating enzyme]-S-ubiquitinyl-L-cysteine;
[acceptor protein]-L-lysine;
[HECT-type E3 ubiquitin transferase]-L-cysteine;
[HECT-type E3 ubiquitin transferase]-S-ubiquitinyl-L-cysteine

In the first step the enzyme transfers ubiquitin from the E2 ubiquitin-conjugating enzyme (EC 2.3.2.23) to a cysteine residue in its HECT domain (which is located in the C-terminal region), forming a thioester bond. In a subsequent step the enzyme transfers the ubiquitin to an acceptor protein, resulting in the formation of an isopeptide bond between the C-terminal glycine residue of ubiquitin and the epsilon-amino group of an L-lysine residue of the acceptor protein. cf. EC 2.3.2.27, RING-type E3 ubiquitin transferase and EC 2.3.2.31, RBR-type E3 ubiquitin transferase.

EC 2.3.2.26 created 2015, modified 2017