Table 1.
Classification of E3 ligases
| Types | Characteristic domains | Member | Subtypes | Characteristic domains of subtypes | Examples |
|---|---|---|---|---|---|
| RINGs | RING fold structure with/without zinc-binding site (RING/U-box) | >600 | Monomers | Monomeric RING/U-box | c-CBL, TRIM11, E4B |
| Homodimers | Homomeric RING/U-box | Chip, SIAH1 | |||
| Heterodimers | Heteromeric RING | MDM2, HaKai | |||
| Cullin-RING ligases (CRLs) | Cullin scaffold structure | SKP1, RBX1, CRL1/2/3/4/5/7/9, FBPs: FBXL, FBXW, FBXO | |||
| Other Multi-subunit E3s | Multiple subunit structure | APC/C | |||
| HECTs | N-terminal lobe, C-terminal lobe, and a flexible tether between two lobes | About 30 | NEDD4 family | Tryptophan-tryptophan (WW) motifs | NEDD4, ITCH, SMURF1, SMURF2 |
| HERC family | RCC1-like domain | HERC1-2, HERC3-6 | |||
| Other HECTs | Various domain | E6AP | |||
| RBRs | Two RING domains and one-in-between-RING (IBR) domain2 | 14 | Ariadne family | Ariadne domain | HHARI, TRIAD1 |
| Other RBRs | Various domain | PAPKIN, HOIL-1L |