Structure‐function studies of the Golgi Dsc E3 ligase complex required for SREBP activation in yeast

Abstract

Fungal sterol regulatory element‐binding protein (SREBP) transcription factors are oxygen‐responsive transcription factors required for adaptation to hypoxia. Our recent studies identified five genes (dsc1–5, defective for SREBP cleavage) that code for subunits of the Golgi Dsc E3 ligase complex that is required for fission yeast SREBP activation. Dsc proteins have domains that are predicted to function in the ubiquitin proteasome pathway: Dsc1 is a ubiquitin E3 ligase with a RING domain, Dsc2 has a predicted ubiquitin‐associated (UBA) domain and Dsc5 contains a ubiquitin regulatory X (UBX) domain that binds Cdc48.To begin to define the mechanism for Sre1 cleavage in fission yeast, we performed structure‐function studies to elucidate the organization of this multi‐subunit complex. Using co‐immunoprecipitation analysis and Blue native PAGE, we found that Dsc1–5 form a stable, detergent solubilized complex with a discrete architecture with distinct subcomplexes. Parallel studies in budding yeast, which lacks SREBP homologs, demonstrate that the Dsc E3 ligase complex is structurally conserved and localizes to the Golgi. Future studies will focus on the identification of additional Dsc E3 ligase substrates and the function of this complex in Golgi protein degradation.Studies were supported by the National Institutes of Health (HL‐077588).