The sterol transporter STARD3 transports sphingosine at ER-lysosome contact sites

Abstract

Sphingolipids are important structural components of membranes. Additionally, simple sphingolipids such as sphingosine are highly bioactive and participate in complex subcellular signaling. Sphingolipid deregulation is associated with many severe diseases including diabetes, Parkinson's and cancer. Here, we focus on how sphingosine, generated from sphingolipid catabolism in late endosomes/lysosomes, is reintegrated into the biosynthetic machinery at the endoplasmic reticulum (ER). We characterized the sterol transporter STARD3 as a sphingosine transporter acting at lysosome-ER contact sites. Experiments featuring crosslinkable sphingosine probes, supported by unbiased molecular dynamics simulations, exposed how sphingosine binds to the lipid-binding domain of STARD3. Following the metabolic fate of pre-localized lysosomal sphingosine showed the importance of STARD3 and its actions at contact sites for the integration of sphingosine into ceramide in a cellular context. Our findings provide the first example of inter-organellar sphingosine transfer and pave the way for a better understanding of sphingolipid - sterol co-regulation.

Single residues in the complexin N-terminus exhibit distinct phenotypes in synaptic vesicle fusion

“…To visualize crosslinks, alkyne PC was labeled with a fluorophore (Alexa 647), using click chemistry and the crosslinked products were analyzed by SDS-PAGE and scanning the Alexa 647 fluorescence (Fig. 1B) (Hempelmann et al, 2023). Lower left panel exemplarily shows alkyne PC crosslinks at positions M5Bpa, A12Bpa, D15Bpa by Alexa 647 fluorescence intensities and the corresponding Cpx bands by Coomassie blue staining.…”

“…For detection of lipid crosslinks (Hempelmann et al, 2023), 22 mol% POPC in the SUV bilayer was replaced by the corresponding amount of alkyne PC (16:0(alkyne)-18:1 PC, Avanti lipids). vSNARE/Syt1-SUVs (5 nmol lipid) and t-SNARE GUVs (28 nmol lipid) were incubated with 6 µM Cpx-WT or BPA mutants in glutathione containing fusion buffer on ice for 30 min to obtain efficient docking and priming as described previously (Malsam et al, 2012).…”

“…To visualize crosslinks, alkyne PC was labeled with a fluorophore (Alexa 647), using click chemistry and the crosslinked products were analyzed by SDS-PAGE and scanning the Alexa 647 fluorescence (Fig. 1B) (Hempelmann et al, 2023)…”

Exploring the lutein therapeutic potential in steatotic liver disease: mechanistic insights and future directions

“…The lutein-binding function of STARD3 resides within the C-terminal START domain as a tunnel-like hydrophobic cavity ( Horvath et al, 2016 ), which can also accommodate a single cholesterol molecule with 1.5 mM affinity. Recently, Hempelmann et al, 2023 elegantly demonstrated the mobilization of sphingosine by STARD3 at inter-organellar level. Therefore, lutein cholesterol and maybe sphingosine share the same protein binding site, with lutein exhibiting a higher affinity.…”