Article

Dual E1 activation systems for ubiquitin differentially regulate E2 enzyme charging

Department of Pathology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115, USA.
Nature (Impact Factor: 42.35). 07/2007; 447(7148):1135-8. DOI: 10.1038/nature05902
Source: PubMed

ABSTRACT Modification of proteins with ubiquitin or ubiquitin-like proteins (UBLs) by means of an E1-E2-E3 cascade controls many signalling networks. Ubiquitin conjugation involves adenylation and thioesterification of the carboxy-terminal carboxylate of ubiquitin by the E1-activating enzyme Ube1 (Uba1 in yeast), followed by ubiquitin transfer to an E2-conjugating enzyme through a transthiolation reaction. Charged E2s function with E3s to ubiquitinate substrates. It is currently thought that Ube1/Uba1 is the sole E1 for charging of E2s with ubiquitin in animals and fungi. Here we identify a divergent E1 in vertebrates and sea urchin, Uba6, which specifically activates ubiquitin but not other UBLs in vitro and in vivo. Human Uba6 and Ube1 have distinct preferences for E2 charging in vitro, and their specificity depends in part on their C-terminal ubiquitin-fold domains, which recruit E2s. In tissue culture cells, Uba6 is required for charging a previously uncharacterized Uba6-specific E2 (Use1), whereas Ube1 is required for charging the cell-cycle E2s Cdc34A and Cdc34B. Our data reveal unexpected complexity in the pathways that control the conjugation of ubiquitin, in which dual E1s orchestrate the charging of distinct cohorts of E2s.

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    • "Such degradation seems to depend both on ubiquitin-activating enzymes and on the 26S proteasome pathway. In the human ubiquitylation pathway, ubiquitin is adenylated either by UBA1 or UBA6, the two only ubiquitin-activating enzymes (Jin et al., 2007). Because the degradation of XPB depends both on ubiquitin-activating enzymes and on the 26S proteasome, we conclude that XPB undergoes rapid ubiquitylation after SP-treatment that leads to its quick degradation by the proteasome pathway. "
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    Chemistry & biology 02/2014; 21(3). DOI:10.1016/j.chembiol.2013.12.014 · 6.59 Impact Factor
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    • "However, owing to the unique topology of UbL73P, we postulated that not all ubiquitin conjugation pathways will utilize it equally. Thus, we asked whether the two human E1 enzymes, Ube1 and Uba6, which have been shown to dictate downstream ubiquitination events in vivo (Jin et al., 2007), showed preference between wild-type and UbL73P. In an in vitro E1 charging reaction, Ube1 and Uba6 differ only slightly in UbL73P charging (Figure 2A); however, Uba6 cannot use UbL73P in charging UbcH7 in an E2-charging reaction (Figure 2B). "
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    Cell Reports 11/2013; 5(3). DOI:10.1016/j.celrep.2013.10.008 · 8.36 Impact Factor
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    • "The only E2 known to be specifically activated by Uba6 is Use1 (Jin et al., 2007). Depletion of Use1 with three independent siRNAs resulted in a 1.6-to 2.4-fold increase in the abundance of Ube3a (Figure 6D, lanes 1–4), independent of its mRNA (Figure 6B). "
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    ABSTRACT: The Uba6 (E1)-Use1 (E2) ubiquitin transfer cascade is a poorly understood alternative arm of the ubiquitin proteasome system (UPS) and is required for mouse embryonic development, independent of the canonical Uba1-E2-E3 pathway. Loss of neuronal Uba6 during embryonic development results in altered patterning of neurons in the hippocampus and the amygdala, decreased dendritic spine density, and numerous behavioral disorders. The levels of the E3 ubiquitin ligase Ube3a (E6-AP) and Shank3, both linked with dendritic spine function, are elevated in the amygdala of Uba6-deficient mice, while levels of the Ube3a substrate Arc are reduced. Uba6 and Use1 promote proteasomal turnover of Ube3a in mouse embryo fibroblasts (MEFs) and catalyze Ube3a ubiquitylation in vitro. These activities occur in parallel with an independent pathway involving Uba1-UbcH7, but in a spatially distinct manner in MEFs. These data reveal an unanticipated role for Uba6 in neuronal development, spine architecture, mouse behavior, and turnover of Ube3a.
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