The E3 ligase HOIP specifies linear ubiquitin chain assembly through its RING-IBR-RING domain and the unique LDD extension

Abstract

The E3 ligase HOIP specifies linear ubiquitin chain assembly through its RING-IBR-RING domain and the unique LDD extensionLike Parkin, the linear ubiquitin chain assembly complex LUBAC functions as a RING/HECT-hybrid ubiquitin ligase, but includes a unique extension that dictates linear ubiquitin linkage specificity.

Parkin mitochondrial translocation is achieved through a novel catalytic activity coupled mechanism

“…The ubiquitin-trapped band of Parkin C431S could only be detected in CCCP-treated WT but not in Pink1-null cells ( Figure 1F), indicating that Pink1 is required for ubiquitin trapping by Parkin. These data suggest that Parkin-mediated mitophagy indeed relies on an intermediate ubiquitin transfer step, consistent with the recent in vitro biochemical findings with the HHARI and HOIP RBR E3 ligases [27][28][29]. The fact that Parkin C431S ubiquitin trapping only happens when mitochondria are depolarized and Pink1 is present, implies that Parkin E3 ligase activity is switched from an inactive to an active state under these conditions, in a manner regulated by Pink1.…”

“…Traditional RING E3 ligases activate direct transfer of ubiquitin from E2~Ub to substrate; in contrast, HECT domain E3 ligases first transfer ubiquitin to a catalytic cysteine before passing it to substrate [26]. It was recently found, however, that HHARI and HOIP, both members of the RBR E3 ligase family, appear to function like HECT domain E3 ligases [27][28][29]. An intermediate cysteine~ubiquitin transfer step can be detected with both the HHARI and HOIP RBR domains in an in vitro assay.…”

The ubiquitin conjugating enzyme UBE2L3 regulates TNFα-induced linear ubiquitination

“…The highly homologous E2 enzyme UBE2D3 (also known as UbcH5C), which can assemble linear ubiquitin chains in vitro [6,8,9], failed to interact with any LUBAC components by co-IP (Supplementary information, Figure S1B). Furthermore, UBE2D3 did not trigger NF-κB reporter activity ( Figure 1A).…”

“…LUBAC is a 600 kDa multimeric complex [6,8,9]. However, the stoichiometry and additional components associated with the LUBAC protein complex remain unknown.…”

The ubiquitin system: a critical regulator of innate immunity and pathogen–host interactions

“…5 As with HECT E3s, RBR E3s control linkage specificity as exemplified by the linear Ub chain assembly complex (LUBAC), which exhibits a unique capacity to synthesize linear Ub chains. 6 As a versatile post-translational protein modification, ubiquitination triggers diverse biological outcomes. The addition of a single Ub typically alters the activity, interaction or localization of the labeled protein, whereas the conjugation of polyubiquitin chains with different linkage types confers distinct functions because of dissimilar topology structures.…”