ASB proteins interact with Cullin5 and Rbx2 to form E3 ubiquitin ligase complexes

FEBS Lett. 2005 Dec 19;579(30):6796-802. doi: 10.1016/j.febslet.2005.11.016. Epub 2005 Nov 28.


The ankyrin repeat and SOCS box (ASB) family is composed of 18 proteins from ASB1 to ASB18 and belongs to the suppressor of cytokine signaling (SOCS) box protein superfamily. ASB2 was recently shown to interact with a certain Cul-Rbx module to form an E3 ubiquitin (Ub) ligase complex, but the functional composition of the ASB-containing E3 Ub ligase complexes remains to be characterized. Here, we show that ASB proteins interact with Cul5-Rbx2 but neither Cul2 nor Rbx1 in cells. Mutational analysis revealed that the highly conserved amino acid sequences of the BC box and Cul5 box in the SOCS box of ASB proteins were essential for the interaction with Cul5-Rbx2. Although ASB proteins show slight divergences from the consensus sequences of the BC box and Cul5 box, all five tested ASB proteins bound to Cul5-Rbx2. Furthermore, all three tested ASB complexes containing Cul5-Rbx2 were found to have E3 Ub ligase activity. These findings suggest that the ASB family proteins interact with Cul5-Rbx2 to form E3 Ub ligases and play significant roles via a ubiquitination-mediated pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Ankyrin Repeat
  • Blotting, Western
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cell Line
  • Cullin Proteins / genetics
  • Cullin Proteins / metabolism*
  • DNA Mutational Analysis
  • Escherichia coli / genetics
  • Humans
  • Ligases / metabolism
  • Molecular Sequence Data
  • Mutation
  • Precipitin Tests
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Sequence Homology, Amino Acid
  • Suppressor of Cytokine Signaling Proteins / chemistry
  • Suppressor of Cytokine Signaling Proteins / genetics
  • Suppressor of Cytokine Signaling Proteins / metabolism*
  • Transfection
  • Ubiquitin-Protein Ligases / biosynthesis*
  • Ubiquitin-Protein Ligases / genetics


  • Carrier Proteins
  • Cullin Proteins
  • Recombinant Proteins
  • Repressor Proteins
  • Suppressor of Cytokine Signaling Proteins
  • RNF7 protein, human
  • Ubiquitin-Protein Ligases
  • Ligases