Research article

Components of the ubiquitin-proteasome pathway compete for surfaces on Rad23 family proteins

Amanda M Goh^1,5 , Kylie J Walters² , Suzanne Elsasser³ , Rati Verma⁴ , Raymond J Deshaies⁴ , Daniel Finley³ and Peter M Howley¹

¹Department of Pathology, Harvard Medical School, Boston, Massachusetts, USA

²Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA

³Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA

⁴Department of Biology, Howard Hughes Medical Institute, California Institute of Technology, Pasadena, California, USA

⁵Institute of Molecular and Cell Biology, Singapore

author email corresponding author email

BMC Biochemistry 2008, 9:4doi:10.1186/1471-2091-9-4

Published:	30 January 2008

Abstract

Background

The delivery of ubiquitinated proteins to the proteasome for degradation is a key step in the regulation of the ubiquitin-proteasome pathway, yet the mechanisms underlying this step are not understood in detail. The Rad23 family of proteins is known to bind ubiquitinated proteins through its two ubiquitin-associated (UBA) domains, and may participate in the delivery of ubiquitinated proteins to the proteasome through docking via the Rad23 ubiquitin-like (UBL) domain.

Results

In this study, we investigate how the interaction between the UBL and UBA domains may modulate ubiquitin recognition and the delivery of ubiquitinated proteins to the proteasome by autoinhibition. We have explored a competitive binding model using specific mutations in the UBL domain. Disrupting the intramolecular UBL-UBA domain interactions in HHR23A indeed potentiates ubiquitin-binding. Additionally, the analogous surface on the Rad23 UBL domain overlaps with that required for interaction with both proteasomes and the ubiquitin ligase Ufd2. We have found that mutation of residues on this surface affects the ability of Rad23 to deliver ubiquitinated proteins to the proteasome.

Conclusion

We conclude that the competition of ubiquitin-proteasome pathway components for surfaces on Rad23 is important for the role of the Rad23 family proteins in proteasomal targeting.