Biology subjects

Lipp, N.-F.

Publications and source records attributed to Lipp, N.-F..

4 recordsLinked to original sources

bioRxiv2025

Transport of sphingolipids by yeast Npc2 supports phase separation of the vacuole membrane

The yeast vacuole membrane forms ordered microdomains that facilitate micro-lipophagy under nutrient limitation. We previously found that this process involves the intracellular sorting of sphingolipids to the vacuole. While multiple vacuole protein pathways have been identified, corresponding mechanisms for lipid sorting remain undefined. Here we use a range of approaches to identify how endocytic sorting and intraluminal transport of sphingolipids contribute to the formation of vacuole domains. To visualize sphingolipid trafficking, we employed the ceramide analogue BODIPY C12-ceramide (BODIPY-Cer), which is internalized by cells and stains the vacuole. We observed that cells lacking Vps29 and Vps30, proteins involved in endosomal sorting, show altered vacuole domains and accumulate BODIPY-Cer at sites proximal to the plasma membrane. Subsequent incorporation of endocytic-derived ceramide into the vacuole is dependent on the Niemann-Pick Type C 2 protein (Npc2). Loss of Npc2 reduces domain formation and causes BODIPY-Cer to accumulate within the vacuole lumen. Both intra-vacuole trafficking of BODIPY-Cer and membrane phase separation were not dependent on Npc2s canonical receptor, Ncr1. Lipidomics of isolated vacuoles confirmed that Npc2 independently mediates sphingolipid sorting under micro-lipophagy conditions. In liposome assays, Npc2 robustly transports analogues of ceramide and inositol phosphorylceramide, a complex sphingolipid that is enriched in phase-separated vacuoles. We propose that the enlarged binding cavity of yeast Npc2 is specialized for the incorporation of sphingolipids into the vacuole membrane.

biochemistry↗

bioRxiv2025

An origin for a eukaryotic lipid transfer protein fold in Asgard archaea

Eukaryotic cells rely on conserved lipid transfer proteins (LTPs) to shuttle insoluble phospholipids between membranes and support organelle proliferation. Because cells lacking organelles do not require extensive lipid transport networks, it is not known if such machinery had to evolve during eukaryogenesis. Here we describe a class of phospholipid transporters in Asgard archaea that share structural and functional features with eukaryotic LTPs of the START domain superfamily. Asgard genomes encode three START protein classes, StarAsg1-3, conserved across most phyla, of which only StarAsg1 has the large hydrophobic cavity and membrane-docking motifs required for lipid transfer. StarAsg1 from Lokiarchaeia binds anionic membranes in vitro and in yeast, extracts phospholipids, and transfers several phospholipid classes between membranes, as eukaryotic START LTPs do. Phylogeny suggests eukaryotic LTPs could share ancestry with StarAsg1, while StarAsg2/3 group with a eukaryotic Hsp90 co-chaperone. Inter-membrane lipid transport may have predated eukaryogenesis and subsequently facilitated organelle proliferation.

evolutionary biology↗

bioRxiv2021

Functional analyses of phosphatidylserine/PI(4)P exchangers with diverse lipid species and membrane contexts set unanticipated rules on lipid transfer

Several members of the oxysterol-binding protein-related proteins (ORPs)/oxysterol-binding homology (Osh) family exchange phosphatidylserine (PS) and phosphatidylinositol 4-phosphate (PI(4)P) at the endoplasmic reticulum/plasma membrane (PM) interface. It is unclear whether they preferentially exchange PS and PI(4)P with specific acyl chains to tune the features of the PM, whether they use phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) instead of PI(4)P for exchange processes and whether their activity is influenced by the association of PS with sterol in the PM. Here, we measured in vitro how the yeast Osh6p and human ORP8 transported diverse PS and PI(4)P subspecies, including major cellular species, between membranes. We established how their activity is impacted by the length and unsaturation degree of these lipids. Surprisingly, the speed at which they individually transfer these ligands inversely depends on their affinity for them. To be fast, the transfer of high-affinity ligands requires their exchange for a counterligand of equivalent affinity. Besides, we determined that Osh6p and ORP8 cannot use PI(4,5)P2 for intracellular lipid exchange, as they have a low affinity for this lipid compared to PI(4)P, and do not transfer more PS into sterol-rich membranes. This study provides insights into PS/PI(4)P exchangers and sets unanticipated rules on how the activity of lipid transfer proteins relates to their affinity for ligands.

biochemistry↗

bioRxiv2020

Osh6 requires Ist2 for localization to the ER-PM contacts and efficient phosphatidylserine transport

Osh6 and Osh7 are lipid transfer proteins (LTPs) that move phosphatidylserine (PS) from the endoplasmic reticulum (ER) to the plasma membrane (PM). High PS level at the PM is key for many cellular functions. Intriguingly, Osh6/7 localize to ER-PM contact sites, although they lack membrane-targeting motifs, in contrast to multidomain LTPs that both bridge membranes and convey lipids. We show that Osh6 localization to contact sites depends on its interaction with the cytosolic tail of the ER-PM tether Ist2, a homologue of TMEM16 proteins. We identify a motif in the Ist2 tail, conserved in yeasts, as the Osh6-binding region, and we map an Ist2-binding surface on Osh6. Mutations in the Ist2 tail phenocopy osh6{Delta} osh7{Delta} deletion: they decrease cellular PS levels, and block PS transport to the PM. Our study unveils an unexpected partnership between a TMEM16-like protein and a soluble LTP, which together mediate lipid transport at contact sites.

cell biology↗