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.



Hansen, K.G., N. Aviram, J. Laborenz, C. Bibi, M. Meyer, A. Spang, M. Schuldiner, and J.M. Herrmann. (2018). An ER surface retrieval pathway safeguards the import of mitochondrial membrane proteins in yeast. Science 361: 1118-1122.


TC#NameOrganismal TypeExample

The ER surface retrieval pathway (ER-SURF) complex (Hansen et al. 2018).
Djp1, ER chaparone protein (P40564)
Ema17 of 142 aas and 2 TMSs (Q40538)
Ema19 of 161 aas and 4 TMSs (Q12155)
Ema35 of 316 aas and an uncertain umber of TMSs (P25606)
Arl1/TGN, Arf-like protein (GTPase) of 183 aas (P38116)
Age2/TGN, Arf-GAP (GTPase) of 298 aas (P40529)
TIM50 (see TC# 3.A.8.1.1)
Aim32 of 311 aas (Q04689)

Other proteins may be involved.

ER-SURF of Saccharomyces cerevisiae