Lea Cecilie Christensen:
Insights on redox active proteins involved in ER-associated degradation

Date: 04-01-2016    Supervisor: Lars Ellgaard

Secretory and membrane proteins are translocated to the endoplasmic reticulum (ER) where they are allowed to adopt their native structure. Posttranslational modifications such as N-glycosylations and disulphide bonds function to stabilise the structure as well as guide the folding process. Still, proteins often fail to adopt their native fold. Such proteins are deemed terminally misfolded and targeted for degradation. The ERassociated degradation (ERAD) pathway takes care of the proper targeting and dislocation of misfolded proteins from the ER to the cytosol. Here, they are degraded by the ubiquitin-proteasome system thereby preventing the otherwise potentially devastating effects of accumulated misfolded proteins. One member of the ERAD pathway is the VCP-interacting membrane protein (VIMP). VIMP is a selenoprotein with a proposed reductase activity. Moreover, VIMP is an ER membrane protein that has been shown to interact with a variety of proteins both implicated in ERAD, but also many other cellular processes. Still, the cellular function of VIMP remains to be elucidated. In this thesis, VIMP’s known interaction with the cytosolic AAA-ATPase p97 was further investigated using nuclear magnetic resonance (NMR). Moreover, the ability of the thioredoxin system to reduce VIMP in vitro was analysed. The degradation of MHC class I heavy chain was analysed for a dependence of VIMP using siRNA knockdown in β2m-deficient cells. Finally, I analysed the redox properties of an uncharacterised protein, which our collaborators identified as having a function in ERAD. Overall, the findings of this thesis add to the field of redox biology associated with the ER. However, experiments are still needed to elucidate the exact function of the investigated proteins.