Two different classes of E2 ubiquitin conjugating enzymes are required for the mono-ubiquitination of proteins and elongation by polyubiquitin chains with a specific topology

Mark Windheim (1) , Mark Peggie , Philip Cohen

1 MRC Protein Phosphorylation Unit

RING and U-box E3 ligases bridge E2 ubiquitin-conjugating enzymes and substrates to enable the transfer of ubiquitin to a lysine residue on the substrate or to one of the seven lysine residues of ubiquitin for polyubiquitin chain elongation. Different polyubiquitin chains have different functions. K48-linked chains target proteins for proteasomal degradation and K63-linked chains function in signal transduction, endocytosis and DNA repair. For this reason, chain topology must be tightly controlled. Using the U-Box E3 ligase CHIP and the RING E3 ligase TRAF6 with the E2s Ubc13-Uev1a and UbcH5a, we demonstrate that Ubc13-Uev1a supports the formation of free K63-linked polyubiquitin chains not attached to CHIP or TRAF6, whereas UbcH5a catalyses the formation of polyubiquitin chains linked to CHIP and TRAF6 that lack specificity for any lysine residue of ubiquitin. Therefore, the abilities of these E2s to ubiquitinate a substrate and to elongate polyubiquitin chains of a specific topology appear to be mutually exclusive. Thus, two different classes of E2 may be required to attach a polyubiquitin chain of a particular topology to a substrate: the properties of one E2 are designed to mono-ubiquitinate a substrate with no or little inherent specificity for an acceptor lysine residue, while the properties of the second E2 are tailored to the elongation of a polyubiquitin chain using a defined lysine residue of ubiquitin.

Mots clés: Life Sciences

Mark Windheim, Mark Peggie, Philip Cohen. Two different classes of E2 ubiquitin conjugating enzymes are required for the mono-ubiquitination of proteins and elongation by polyubiquitin chains with a specific topology. Biochemical Journal, 2007, 409 (3), pp.723-729. ⟨10.1042/BJ20071338⟩. ⟨hal-00478887⟩