EMC Is Required to Initiate Accurate Membrane Protein Topogenesis

Cell. 2018 Nov 29;175(6):1507-1519.e16. doi: 10.1016/j.cell.2018.10.009. Epub 2018 Nov 8.


Mammals encode ∼5,000 integral membrane proteins that need to be inserted in a defined topology at the endoplasmic reticulum (ER) membrane by mechanisms that are incompletely understood. Here, we found that efficient biogenesis of β1-adrenergic receptor (β1AR) and other G protein-coupled receptors (GPCRs) requires the conserved ER membrane protein complex (EMC). Reconstitution studies of β1AR biogenesis narrowed the EMC requirement to the co-translational insertion of the first transmembrane domain (TMD). Without EMC, a proportion of TMD1 inserted in an inverted orientation or failed altogether. Purified EMC and SRP receptor were sufficient for correctly oriented TMD1 insertion, while the Sec61 translocon was necessary for insertion of the next TMD. Enforcing TMD1 topology with an N-terminal signal peptide bypassed the EMC requirement for insertion in vitro and restored efficient biogenesis of multiple GPCRs in EMC-knockout cells. Thus, EMC inserts TMDs co-translationally and cooperates with the Sec61 translocon to ensure accurate topogenesis of many membrane proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line, Tumor
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism*
  • Female
  • Humans
  • Intracellular Membranes / metabolism*
  • Protein Domains
  • Protein Transport / physiology
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Receptors, Peptide / genetics
  • Receptors, Peptide / metabolism*
  • SEC Translocation Channels / genetics
  • SEC Translocation Channels / metabolism*
  • Turkeys


  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Peptide
  • SEC Translocation Channels
  • signal peptide receptor