Dissection of the Erv41‐Erv46 retrieval pathway suggests a redox‐regulated mechanism

Abstract

The early secretory pathway consists of ER‐ and Golgi‐resident proteins involved in synthesis, folding, quality control, and post translational modifications of secretory proteins. Anterograde flux through this pathway can lead to the mislocalization of ER‐resident proteins as they passively leak to the Golgi. Fortunately there are several retrieval mechanisms to return mislocalized ER‐residents back to the ER. One such retrieval process identified by our lab relies on the Erv41‐Erv46 complex, which recognizes specific non‐HDEL ER‐residents in the Golgi and returns them to the ER in a COPI‐dependent manner. The focus of our work is to determine the mechanism by which the Erv41‐Erv46 retrograde receptor binds to escaped ER‐residents in the Golgi and releases this cargo in the ER.Site‐directed mutagenesis to introduce Erv41 and Erv46 mutations in Saccharomyces cerevisiae revealed key residues involved in retrieval of non‐HDEL ER‐residents. One such series of mutations involves a cysteine rich region of Erv46 where Cys to Ser mutants result in a complete loss of function. This cysteine rich region contains two CXXC motifs typically found in redox proteins. As observed in other redox proteins, the residues between the vicinal cysteines in this region of Erv46 are important suggesting that the redox potential of these cysteines is finely tuned for activity. Furthermore, mutations of a four residue hydrophobic patch within the cysteine rich region as well as a distal basic residue in Erv46 leads to a failure in retrieval of ER‐residents. These residues, but not the cysteines, are conserved in Erv41, however concomitant mutations in Erv41 do not affect retrieval suggesting Erv46 is predominantly involved in binding while Erv41 may play a distinct role.Based on our results, we propose the redox state of Erv46 is highly dynamic resulting in active and inactive disulfide configurations which can expose or mask a cargo binding hydrophobic patch. Defining the Erv41‐Erv46 binding mechanism may allow for a more complete understanding of ER homeostasis as well as providing a potential target to block pathogenic toxins that exploit Erv41‐Erv46 mediated retrieval for efficient delivery to the ER.Support or Funding InformationNIH GM52549This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.