Variation on a Theme

Science's STKE  05 Jul 2005:
Vol. 2005, Issue 291, pp. tw246
DOI: 10.1126/stke.2912005tw246

Ubiquitination is a protein modification used by eukaryotic cells to regulate a broad range of cellular functions. So far, E3-ubiquitin ligases have only been known to catalyze the formation of an isopeptide bond between ubiquitin and a lysine (or the N terminus) of the substrate. Cadwell and Coscoy show that MIR1, a virally encoded E3-ubiquitin ligase, promotes ubiquitination of its substrate by a novel and unexpected mechanism. Ubiquitination of major histocompatibility complex class I (MHC-I) molecules by MIR1 does not involve an isopeptide bond but rather a thiol-ester bond at a unique cysteine residue encoded within the MHC-I intracytoplasmic domain. This finding broadens the range of candidate substrates for a potentially reversible form of ubiquitination.

K. Cadwell, L. Coscoy, Ubiquitination on nonlysine residues by a viral E3 ubiquitin ligase. Science 309, 127-130 (2005). [Abstract] [Full Text]