Doa1 Is a Cdc48 Adapter That Possesses a Novel Ubiquitin Binding Domain

Abstract

Cdc48 (p97/VCP) is an AAA-ATPase molecular chaperone whose cellular functions are facilitated by its interaction with ubiquitin binding cofactors (e.g., Npl4-Ufd1 and Shp1). Several studies have shown that Saccharomyces cerevisiae Doa1 (Ufd3/Zzz4) and its mammalian homologue, PLAA, interact with Cdc48. However, the function of this interaction has not been determined, nor has a physiological link between these proteins been demonstrated. Herein, we demonstrate that Cdc48 interacts directly with the C-terminal PUL domain of Doa1. We find that Doa1 possesses a novel ubiquitin binding domain (we propose the name PFU domain, for PLAA family ubiquitin binding domain), which appears to be necessary for Doa1 function. Our data suggest that the PUL and PFU domains of Doa1 promote the formation of a Doa1-Cdc48-ubiquitin ternary complex, potentially allowing for the recruitment of ubiquitinated proteins to Cdc48. DOA1 and CDC48 mutations are epistatic, suggesting that their interaction is physiologically relevant. Lastly, we provide evidence of functional conservation within the PLAA family by showing that a human-yeast chimera binds to ubiquitin and complements doa1Δ phenotypes in yeast. Combined, our data suggest that Doa1 plays a physiological role as a ubiquitin binding cofactor of Cdc48 and that human PLAA may play an analogous role via its interaction with p97/VCP.

We thank members of the Wilkinson Lab for critical reading of the manuscript, Michel Ghislain (Universite Catholique de Louvain) for the HisFlag-Doa1 constructs, Arun Seth (University of Toronto) for the human PLAA clone, David Botstein (Stanford University School of Medicine) for the DBY469 and DBY1247 yeast cell lines, Mark Hochstrasser (Yale University) for the MHY501 yeast cell line, Dan Finley (Harvard University) for the ubiquitin expression vector, Judith Fridovich-Keil (Emory University School of Medicine) for the pYEPGAP vector, and Mark Longtine (Oklahoma State University) for the gene disruption vectors.

This work was supported by a postdoctoral fellowship from the American Heart Association and NIH grant R01-GM30308.