The endoplasmic reticulum membrane protein complex localizes to the mitochondrial - endoplasmic reticulum interface and its subunits modulate phospholipid biosynthesis in Trypanosoma brucei

PLoS Pathog. 2022 May 2;18(5):e1009717. doi: 10.1371/journal.ppat.1009717. eCollection 2022 May.

Abstract

The endoplasmic reticulum membrane complex (EMC) is a versatile complex that plays a key role in membrane protein biogenesis in the ER. Deletion of the complex has wide-ranging consequences including ER stress, disturbance in lipid transport and organelle tethering, among others. Here we report the function and organization of the evolutionarily conserved EMC (TbEMC) in the highly diverged eukaryote, Trypanosoma brucei. Using (co-) immunoprecipitation experiments in combination with mass spectrometry and whole cell proteomic analyses of parasites after depletion of select TbEMC subunits, we demonstrate that the TbEMC is composed of 9 subunits that are present in a high molecular mass complex localizing to the mitochondrial-endoplasmic reticulum interface. Knocking out or knocking down of single TbEMC subunits led to growth defects of T. brucei procyclic forms in culture. Interestingly, we found that depletion of individual TbEMC subunits lead to disruption of de novo synthesis of phosphatidylcholine (PC) or phosphatidylethanolamine (PE), the two most abundant phospholipid classes in T. brucei. Downregulation of TbEMC1 or TbEMC3 inhibited formation of PC while depletion of TbEMC8 inhibited PE synthesis, pointing to a role of the TbEMC in phospholipid synthesis. In addition, we found that in TbEMC7 knock-out parasites, TbEMC3 is released from the complex, implying that TbEMC7 is essential for the formation or the maintenance of the TbEMC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Endoplasmic Reticulum / metabolism
  • Membrane Proteins / metabolism
  • Phospholipids / metabolism
  • Proteomics
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism
  • Trypanosoma brucei brucei* / metabolism

Substances

  • Membrane Proteins
  • Phospholipids
  • Protozoan Proteins

Grants and funding

This work was supported by Swiss National Science Foundation grants 169355 (PB) and 175563 (AS), Swiss National Science Foundation NCCR "RNA & Disease" (AS), Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) project ID 403222702/SFB 1381 (BW) and Germany’s Excellence Strategy CIBSS – EXC-2189 – project ID 390939984 (BW). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.