A MUB E2 structure reveals E1 selectivity between cognate ubiquitin E2s in eukaryotes.

Ubiquitin (Ub) is a protein modifier that controls processes ranging from protein degradation to endocytosis, but early-acting regulators of the three-enzyme ubiquitylation cascade are unknown. Here we report that the prenylated membrane-anchored ubiquitin-fold protein (MUB) is an early-acting regulator of subfamily-specific E2 activation. An AtMUB3:AtUBC8 co-crystal structure defines how MUBs inhibit E2∼Ub formation using a combination of E2 backside binding and a MUB-unique lap-bar loop to block E1 access.

Arabidopsis membrane-anchored ubiquitin-fold (MUB) proteins localize a specific subset of ubiquitin-conjugating (E2) enzymes to the plasma membrane.

The covalent attachment of ubiquitin (Ub) to various intracellular proteins plays important roles in altering the function, localization, processing, and degradation of the modified target. A minimal ubiquitylation pathway uses a three-enzyme cascade (E1, E2, and E3) to activate Ub and select target proteins for modification. Although diverse E3 families provide much of the target specificity, several factors have emerged recently that coordinate the subcellular localization of the ubiquitylation machinery.

MUBs, a family of ubiquitin-fold proteins that are plasma membrane-anchored by prenylation.

Ubiquitin (Ub)-fold proteins are rapidly emerging as an important class of eukaryotic modifiers, which often exert their influence by post-translational addition to other intracellular proteins. Despite assuming a common beta-grasp three-dimensional structure, their functions are highly diverse because of distinct surface features and targets and include tagging proteins for selective breakdown, nuclear import, autophagic recycling, vesicular trafficking, polarized morphogenesis, and the stress response. Here we describe a novel family of Membrane-anchored Ub-fold (MUB) proteins that are present in animals, filamentous fungi, and plants.

The HECT ubiquitin-protein ligase (UPL) family in Arabidopsis: UPL3 has a specific role in trichome development.

Attachment of one or more ubiquitins (Ubs) to various intracellular proteins has a number of roles in plants including the selective removal of regulatory proteins by the 26S proteasome. The final step in this modification is performed by ubiquitin-protein ligases (E3s) that promote Ub transfer to appropriate targets. One important family of E3s is defined by the presence of a HECT domain, an active site first found at the C-terminus of the human E3 (E6-AP).

Identification of an allele of CLA1 associated with variegation in Arabidopsis thaliana.

We have identified a mutant of Arabidopsis thaliana (lvr111) that exhibits a variegated phenotype, reduced isoprenoid pigmentation, and dwarfism in comparison with wild-type plants. Segregation analysis indicated that this phenotype was caused by a single, semi-dominant mutation and PCR-based marker mapping placed the mutation near position 56 on the RI map of chromosome IV. The lvr111 lesion was identified by genomic PCR and sequence analysis as a missense mutation (D306N) in the CLA1 gene (AT4g15560) and complementation analysis confirmed the allelic relationship between lvr111 and CLA1.

The F-box subunit of the SCF E3 complex is encoded by a diverse superfamily of genes in Arabidopsis.

The covalent attachment of ubiquitin is an important determinant for selective protein degradation by the 26S proteasome in plants and animals. The specificity of ubiquitination is often controlled by ubiquitin-protein ligases (or E3s), which facilitate the transfer of ubiquitin to appropriate targets. One ligase type, the SCF E3s are composed of four proteins, cullin1/Cdc53, Rbx1/Roc1/Hrt1, Skp1, and an F-box protein.