title: Non-canonical ubiquitylation of the proneural protein Ngn2 occurs in both Xenopus embryos and mammalian cells.
abstract: Poly-ubiquitin chains targeting proteins for 26S proteasomal degradation are classically anchored on internal lysines of substrates via iso-peptide linkages. However recently, linkage of ubiquitin moieties to non-canonical nucleophilic residues, such as cysteines, serines and threonines, has been demonstrated in a small number of cases. Non-canonical ubiquitylation of the proneural protein Ngn2 has previously been seen in Xenopus egg extract, but it was not clear whether such highly unusual modes of ubiquitylation were restricted to the environment of egg cytoplasm. Here we show that Ngn2 is, indeed, ubiquitylated on non-canonical sites in extracts from neurula stage Xenopus embryos, when Ngn2 is usually active. Moreover, in the P19 mammalian embryonal carcinoma cell line capable of differentiating into neurons, xNgn2 is ubiquitylated on both canonical and non-canonical sites. We see that mutation of cysteines alone results stabilisation of the protein in P19 cells, indicating that non-canonical ubiquitylation on these residues normally contributes to the fast turnover of xNgn2 in mammalian cells.
authors.affiliation: Department of Oncology, University of Cambridge, Hutchison/Medical Research Council (MRC) Research Centre, Addenbrooke's Hospital, Cambridge CB2 0XZ, UK. gsm26@cam.ac.uk
authors.forename: Gary S
authors.initials: GS
authors.lastname: McDowell
authors.forename: Romana
authors.initials: R
authors.lastname: Kucerova
authors.forename: Anna
authors.initials: A
authors.lastname: Philpott
mesh_terms: D000818:Animals; D004625:Embryo, Nonmammalian; D005260:Female; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D054875:Ubiquitination; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: C553500:NEUROG2 protein, Xenopus; D009419:Nerve Tissue Proteins; D029867:Xenopus Proteins; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease