The O-GlcNAc cycling in neurodevelopment and associated diseases.

Proper neuronal development is essential to growth and adult brain function. Alterations at any step of this highly organized sequence of events, due to genetic mutations or environmental factors, triggers brain malformations, which are leading causes of diseases including epilepsy, intellectual disabilities, and many others. The role of glycosylation in neuronal development has been emphasized for many years, notably in studying human congenital disorders of glycosylation (CDGs).

Comprehensive analysis of the human ESCRT-III-MIT domain interactome reveals new cofactors for cytokinetic abscission.

The 12 related human ESCRT-III proteins form filaments that constrict membranes and mediate fission, including during cytokinetic abscission. The C-terminal tails of polymerized ESCRT-III subunits also bind proteins that contain Microtubule-Interacting and Trafficking (MIT) domains. MIT domains can interact with ESCRT-III tails in many different ways to create a complex binding code that is used to recruit essential cofactors to sites of ESCRT activity.

A cancer-associated polymorphism in ESCRT-III disrupts the abscission checkpoint and promotes genome instability.

Cytokinetic abscission facilitates the irreversible separation of daughter cells. This process requires the endosomal-sorting complexes required for transport (ESCRT) machinery and is tightly regulated by charged multivesicular body protein 4C (CHMP4C), an ESCRT-III subunit that engages the abscission checkpoint (NoCut) in response to mitotic problems such as persisting chromatin bridges within the midbody. Importantly, a human polymorphism in CHMP4C (rs35094336, CHMP4C) increases cancer susceptibility.

ULK3 regulates cytokinetic abscission by phosphorylating ESCRT-III proteins.

The endosomal sorting complexes required for transport (ESCRT) machinery mediates the physical separation between daughter cells during cytokinetic abscission. This process is regulated by the abscission checkpoint, a genome protection mechanism that relies on Aurora B and the ESCRT-III subunit CHMP4C to delay abscission in response to chromosome missegregation. In this study, we show that Unc-51-like kinase 3 (ULK3) phosphorylates and binds ESCRT-III subunits via tandem MIT domains, and thereby, delays abscission in response to lagging chromosomes, nuclear pore defects, and tension forces at the midbody.

Intrinsic disorder drives N-terminal ubiquitination by Ube2w.

Ubiquitination of the αN-terminus of protein substrates has been reported sporadically since the early 1980s. However, the identity of an enzyme responsible for this unique ubiquitin (Ub) modification has only recently been elucidated. We show the Ub-conjugating enzyme (E2) Ube2w uses a unique mechanism to facilitate the specific ubiquitination of the α-amino group of its substrates that involves recognition of backbone atoms of intrinsically disordered N termini.

Biochemical and structural characterization of the ubiquitin-conjugating enzyme UBE2W reveals the formation of a noncovalent homodimer.

The biochemical and structural characterization of ubiquitin-conjugating enzymes (E2s) over the past 30 years has fostered important insights into ubiquitin transfer mechanisms. Although many of these enzymes share high sequence and structural conservation, their functional roles in the cell are decidedly diverse. Here, we report that the mono-ubiquitinating E2 UBE2W forms a homodimer using two distinct protein surfaces.

Interactions of the human LIP5 regulatory protein with endosomal sorting complexes required for transport.

The endosomal sorting complex required for transport (ESCRT) pathway remodels membranes during multivesicular body biogenesis, the abscission stage of cytokinesis, and enveloped virus budding. The ESCRT-III and VPS4 ATPase complexes catalyze the membrane fission events associated with these processes, and the LIP5 protein helps regulate their interactions by binding directly to a subset of ESCRT-III proteins and to VPS4. We have investigated the biochemical and structural basis for different LIP5-ligand interactions and show that the first microtubule-interacting and trafficking (MIT) module of the tandem LIP5 MIT domain binds CHMP1B (and other ESCRT-III proteins) through canonical type 1 MIT-interacting motif (MIM1) interactions.

Following Ariadne's thread: a new perspective on RBR ubiquitin ligases.

Ubiquitin signaling pathways rely on E3 ligases for effecting the final transfer of ubiquitin from E2 ubiquitin conjugating enzymes to a protein target. Here we re-evaluate the hybrid RING/HECT mechanism used by the E3 family RING-between-RINGs (RBRs) to transfer ubiquitin to substrates. We place RBRs into the context of current knowledge of HECT and RING E3s.

UBCH7 reactivity profile reveals parkin and HHARI to be RING/HECT hybrids.

Although the functional interaction between ubiquitin-conjugating enzymes (E2s) and ubiquitin ligases (E3s) is essential in ubiquitin (Ub) signalling, the criteria that define an active E2-E3 pair are not well established. The human E2 UBCH7 (also known as UBE2L3) shows broad specificity for HECT-type E3s, but often fails to function with RING E3s in vitro despite forming specific complexes. Structural comparisons of inactive UBCH7-RING complexes with active UBCH5-RING complexes reveal no defining differences, highlighting a gap in our understanding of Ub transfer.

E2s: structurally economical and functionally replete.

Ubiquitination is a post-translational modification pathway involved in myriad cellular regulation and disease pathways. The Ub (ubiquitin) transfer cascade requires three enzyme activities: a Ub-activating (E1) enzyme, a Ub-conjugating (E2) enzyme, and a Ub ligase (E3). Because the E2 is responsible both for E3 selection and substrate modification, E2s function at the heart of the Ub transfer pathway and are responsible for much of the diversity of Ub cellular signalling.