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Free keywords:
CASEIN KINASE-II; CATABOLITE DEGRADATION; BETA-CATENIN; GID COMPLEX;
YEAST GENES; E3 LIGASE; UBIQUITIN; MECHANISM;
FRUCTOSE-1,6-BISPHOSPHATASE; ACTIVATIONBiochemistry & Molecular Biology; Cell Biology;
Abstract:
Ubiquitylation is catalyzed by coordinated actions of E3 and E2 enzymes. Molecular principles governing many important E3 -E2 partnerships remain unknown, including those for RING -family GID/CTLH E3 ubiquitin ligases and their dedicated E2, Ubc8/UBE2H (yeast/human nomenclature). GID/CTLH-Ubc8/UBE2H-mediated ubiquitylation regulates biological processes ranging from yeast metabolic signaling to human development. Here, cryoelectron microscopy (cryo-EM), biochemistry, and cell biology reveal this exquisitely specific E3 -E2 pairing through an unconventional catalytic assembly and auxiliary interactions 70-100 A away, mediated by E2 multisite phosphorylation. Rather than dynamic polyelectrostatic interactions reported for other ubiquitylation complexes, multiple Ubc8/UBE2H phosphorylation sites within acidic CK2-targeted sequences specifically anchor the E2 C termini to E3 basic patches. Positions of phospho-dependent interactions relative to the catalytic domains correlate across evolution. Overall, our data show that phosphorylation-dependent multivalency establishes a specific E3 -E2 partnership, is antagonistic with dephosphorylation, rigidifies the catalytic centers within a flexing GID E3 -substrate assembly, and facilitates substrate collision with ubiquitylation active sites.
