3.A.27.1.2
ER membrane protein insertase complex of eight recognized proteins, EMC1 - 7 + EMC10 (Bai et al. 2020). These authors have determined the high resolution structure of the complex.  It co-translationally inserts TMSs of many multi-pass integral membrane proteins into the ER membrane, and it is also responsible for inserting the TMSs of some tail-anchored proteins. Bai et al. 2020 reported theCryoEM structure. The Saccharomyces cerevisiae EMC contains eight subunits (Emc1-6, Emc7 and Emc10), has a large lumenal region and a smaller cytosolic region, and has a transmembrane region formed by Emc4, Emc5 and Emc6 plus the transmembrane domains of Emc1 and Emc3. They identified a five-TMS fold centred around Emc3 that resembles the prokaryotic YidC insertase and that delineates a largely hydrophilic protein pocket. The transmembrane domain of Emc4 tilts away from the main transmembrane region of EMC and is partially mobile. The flexibility of Emc4 and the hydrophilicity of the pocket are required for EMC function. The structure reveals notable evolutionary conservation with prokaryotic insertases, suggesting that eukaryotic TMS insertion involves a similar mechanism (Bai et al. 2020).