UCLA

The selective removal of damaged or misfolded outer mitochondrial membrane (OMM) proteins is a necessary process to avoid total organelle destruction by mitophagy. This sensing system is called outer mitochondrial membrane associated degradation (OMMAD) and is poorly understood. OMMAD uses the ubiquitin proteasome system (UPS), much like endoplasmic reticulum associated degradation (ERAD), but the specific players composing the pathway are unknown. In this study, we sought to identify some of these components by appending a promiscuous biotin ligase, BirA, to the OMM protein SLC25A46, known to be degraded by this pathway when mutated at a single point. As controls for unspecific biotinylation, we created BirA-MCherry and Mid49-BirA constructs, for the cytosol and OMM, respectively. Mass spectrometry analysis led to the discovery of a potentially novel pathway for OMM protein degradation via the ER. This conclusion is supported by Percoll gradient centrifugation studies indicating the presence of mutated SLC25A46 in the endoplasmic reticulum (ER).