van Schie, S. N. S. | Search bioRxiv

bioRxiv2024

Compositional Flexibility of the ER-Mitochondria Encounter Structure

Yeast mitochondria receive the majority of their lipids from the endoplasmic reticulum (ER) via the heterotetrameric ERMES lipid transport complex. This complex is thought to establish a lipid transporting tube of fixed composition spanning the space between both organelles. Intriguingly, however, some of the lipid-transporting components of the complex can be replaced by an artificial ER-mitochondria tether without lipid transport activity, indicating that ERMES subunits are not all of equal importance for lipid transport. Here, we propose a model whereby lipid transfer by the ERMES complex can occur with various sub-ensembles of ERMES, and minimally with only one of the four members, namely Mmm1. Our results imply flexibility in the composition of the ERMES complex, which might help it accommodate various interorganelle distances.

cell biology↗

bioRxiv2021

Rewiring phospholipid biosynthesis reveals robustness in membrane homeostasis and uncovers lipid regulatory players.

Intracellular transport of lipids by Lipid Transport Proteins (LTPs) is thought to work alongside vesicular transport to shuttle lipids from their place of synthesis to their destinations. Whereas many LTPs have been identified, it is largely unknown which routes and which LTPs a given lipid utilizes to navigate the multiple membranes of eukaryotic cells. The major and essential phospholipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC) can be produced by multiple pathways and, in the case of PE, also at multiple locations. Here, we present an approach in which we simplify and rewire yeast phospholipid synthesis by redirecting PE and PC synthesis reactions to distinct subcellular locations using chimeric enzymes fused to specific organelle targeting motifs. In rewired conditions, viability is expected to depend on homeostatic adaptation to the ensuing lipostatic perturbations and on efficient interorganelle lipid transport. We therefore performed genetic screens to identify factors involved in both of these processes. Among the candidates identified, we find genes linked to transcriptional regulation of lipid homeostasis, lipid metabolism and transport. In particular, we identify a requirement for Csf1 -an uncharacterized protein harboring a Chorein-N lipid transport domain- for survival under certain rewired conditions as well as lipidomic adaptation to cold, implicating Csf1 in interorganelle lipid transport and homeostatic adaptation.

cell biology↗