Abstract
The recently discovered endoplasmic reticulum (ER) membrane protein complex (EMC) has been implicated in ER-associated degradation (ERAD), lipid transport and tethering between the ER and mitochondrial outer membranes, and assembly of multipass ER-membrane proteins. The EMC has been studied in both animals and fungi but its presence outside the Opisthokont clade (animals + fungi + related protists) has not been demonstrated. Here, using homology-searching algorithms, I show that the EMC is truly an ancient and conserved protein complex, present in every major eukaryotic lineage. Very few organisms have completely lost the EMC, and most, even over 2 billion years of eukaryote evolution, have retained a majority of the complex members. I identify Sop4 and YDR056C in Saccharomyces cerevisiae as Emc7 and Emc10, respectively, subunits previously thought to be specific to animals. This study demonstrates that the EMC was present in the last eukaryote common ancestor (LECA) and is an extremely important component of eukaryotic cells even though its primary function remains elusive.
Highlights
Recent studies suggest that the endoplasmic reticulum (ER) membrane protein complex (EMC) (Endoplasmic Reticulum Membrane Complex) is a multifunctional, multi-subunit protein complex
It has been shown that the EMC is an ER-mitochondria tether in S. cerevisiae that interacts with the outer membrane protein Tom5 of the TOM (Translocase of the Mitochondrial Outer Membrane) complex (Lahiri et al, 2014)
These recent findings suggest that EMC involvement in ER-associated degradation (ERAD) may be due to secondary effects, as cells devoid of EMC components may result in either disruption of ER-mitochondria tethering, or the misfolding of multipass membrane proteins
Summary
Recent studies suggest that the EMC (Endoplasmic Reticulum Membrane Complex) is a multifunctional, multi-subunit protein complex. The EMC has been implicated in the proper assembly of multi-pass transmembrane (TM) proteins (Satoh et al, 2015). These recent findings suggest that EMC involvement in ERAD may be due to secondary effects, as cells devoid of EMC components may result in either disruption of ER-mitochondria tethering, or the misfolding of multipass membrane proteins. Since the clade comprising animals and fungi only accounts for one fifth of the diversity of eukaryotes (Adl et al, 2012), more work is necessary in order to support the claim made by Lahiri et al I was prompted to investigate the taxonomic distribution of the EMC in order to (1) determine if it really is a conserved protein complex and (2) if it could possibly represent the pan-eukaryotic ER-mitochondria tether
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