3.A.30.  The Endoplasmic Reticulum Surface Retrieval Pathway (ER-SURF) Family for Mitochondrial Membrane Protein Targeting 

The majority of organellar proteins are translated on cytosolic ribosomes and must be sorted correctly to function. Targeting routes have been identified for organelles such as peroxisomes and the endoplasmic reticulum (ER), and the ER-SURF family may accompllish the initial steps of targeting of integral membrane proteins to the mitochondrial inner membrane. Hansen et al. 2018 used a genome-wide screen in yeast and identified factors critical for the intracellular sorting of the mitochondrial inner membrane protein Oxa1 TC# 2.A.9.1.1). The screen uncovered an unexpected path, termed ER-SURF, for targeting of mitochondrial membrane proteins from the ER to mitochondria. This pathway retrieves mitochondrial proteins from the ER surface and reroutes them to mitochondria with the aid of the ER-localized chaperone, Djp1. Hence, cells use the expanse of the ER surfaces as a fail-safe to maximize productive mitochondrial protein targeting.