Means of self-preservation: how an intrinsically disordered ubiquitin-protein ligase averts self-destruction.
Ubiquitin-protein ligases (E3s) that ubiquitinate substrates for proteasomal degradation are often in the position of ubiquitinating themselves due to interactions with a charged ubiquitin-conjugating enzyme (E2). This can mediate the E3's proteasomal degradation. Many E3s have evolved means to avoid autoubiquitination, including protection by partner or substrate binding, preventative modifications, and deubiquitinating enzyme reversal of ubiquitination. Here we describe another adaptation for E3 self-protection discovered while exploring San1, which ubiquitinates misfolded nuclear proteins in yeast for proteasomal degradation. San1 is highly disordered in its substrate-binding regions N- and C-terminal to its RING domain. In cis autoubiquitination could occur if these flexible regions come in proximity to the E2. San1 prevents this by containing no lysines in its disordered regions; thus the canonical residue used for ubiquitin attachment has been selectively eliminated. San1's target substrates have lost their native structures and expose hydrophobicity. To avoid in trans autoubiquitination, San1 possesses little concentrated hydrophobicity in its disordered regions, and thus the that feature San1 recognizes in misfolded substrates has also been selectively eliminated. Overall the presence of key residues in San1 have been evolutionarily minimized to avoid self-destruction either in cis or in trans. Our work expands the ways in which E3s protect themselves from autoubiquitination.
Department of Pharmacology, University of Washington, Seattle, WA 98195, USA.
Eric K
EK
Fredrickson
Sarah V
SV
Clowes Candadai
Cheuk Ho
CH
Tam
Richard G
RG
Gardner
D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D057927:Hydrophobic and Hydrophilic Interactions; D008239:Lysine / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D055550:Protein Stability; D059748:Proteolysis; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C500396:SAN1 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; D008239:Lysine