EMC7

EMC7 is a constitutive subunit of the conserved ER membrane complex (EMC), an eight-subunit transmembrane-domain insertase of the endoplasmic reticulum (PMID:32494008). Within the complex, EMC7 contributes to an assembly centered on a five-TMH fold resembling the prokaryotic YidC insertase that forms a hydrophilic client pocket for inserting transmembrane helices into the ER membrane (PMID:32494008). Beyond its structural role in the EMC, EMC7 acts as a molecular tether at late endosome–ER membrane contact sites: it engages LE-associated Rab7 and binds the ER-resident fusion machinery component syntaxin18, thereby promoting LE-to-ER cargo targeting, as demonstrated for the entry of SV40 polyomavirus (PMID:32111841). Beyond these roles, the broader functional repertoire of EMC7 has not been characterized in the available corpus.

1. 2011 Low

   An early question was where the uncharacterized C15orf24 (EMC7) protein resides in tissue; immunolocalization placed it at the postsynaptic sarcolemma of the neuromuscular junction, giving a first anatomical foothold.

   Evidence Antibody generation and immunolocalization at murine neuromuscular junction sections

   PMID:21429463

   Open questions at the time

   • Single localization experiment with no functional consequence established
   • No molecular activity or interaction partner defined
   • Does not connect the protein to any pathway
2. 2013 Low

   To find candidate interactors, a split-ubiquitin screen identified the Na+/Mg2+ exchanger SLC41A1 as a transient ER-context binding partner of EMC7, hinting at an ER membrane role.

   Evidence Split-ubiquitin yeast two-hybrid assay

   PMID:23823179

   Open questions at the time

   • Single method (yeast two-hybrid) not confirmed by mass spectrometry or reciprocal co-IP
   • Interaction described as transient, functional significance unclear
   • Does not establish whether the interaction reflects EMC client handling
3. 2020 High

   The molecular function of EMC7 was resolved by placing it within the EMC: cryo-EM showed it is one of eight subunits of a transmembrane-domain insertase whose YidC-like fold creates a hydrophilic pocket for TMH insertion into the ER membrane.

   Evidence Cryo-EM structure of the yeast EMC with mutational validation of client-pocket hydrophilicity and Emc4 flexibility

   PMID:32494008

   Open questions at the time

   • Structure does not define the specific contribution of EMC7 to client insertion
   • Substrate repertoire handled with EMC7 participation not enumerated
   • Human EMC7 inferred from yeast complex architecture
4. 2020 Medium

   A distinct, EMC-independent role emerged when EMC7 was shown to tether late endosomes to the ER by binding Rab7 and syntaxin18, enabling LE-to-ER cargo transport exploited during SV40 entry.

   Evidence Knockdown with SV40 infection assays, co-immunoprecipitation of EMC7 with Rab7 and syntaxin18, and organelle transport assays

   PMID:32111841

   Open questions at the time

   • Co-IP partners identified in a single lab without reciprocal structural validation of the tether
   • Whether tethering activity is separable from EMC subunit function is unresolved
   • Generality beyond SV40 cargo not established

• How the EMC insertase activity of EMC7 relates mechanistically to its endosome-ER tethering role, and whether both functions operate simultaneously in the same cells, remains unresolved.
• No structural model of the EMC7-Rab7-syntaxin18 tether
• Native client substrates of the human EMC requiring EMC7 not defined
• Functional significance of NMJ localization and SLC41A1 interaction unintegrated