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

The covalent attachment of the ubiquitin (Ub) protein 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. While diverse E3 families provide much of the target specificity, several factors have emerged recently that coordinate the subcellular localization of the ubiquitylation machinery. Here we show that the family of Membrane-anchored Ubiquitin-fold (MUB) proteins, structurally related to Ub, recruit and dock specific E2s to the plasma membrane. Protein interaction screens with Arabidopsis MUBs reveal that interacting E2s are limited to a well-defined subgroup that is phylogenetically related to human UbcH5 and yeast Ubc4/5 families. MUBs appear to interact non-covalently with an E2 surface opposite the active site that forms a covalent linkage with Ub. Bimolecular fluorescence complementation (BiFC) demonstrates that MUBs bind simultaneously to the plasma membrane via a prenyl tail and to the E2 in planta. These findings suggest that MUBs contribute subcellular specificity to ubiquitylation by docking the conjugation machinery to the plasma membrane.
Date: Feb. 23, 2011
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