Biology subjects

Schmieder, S. S.

Publications and source records attributed to Schmieder, S. S..

3 recordsLinked to original sources

bioRxiv2025

Palmitoylated caveolin-1 enables endosome sorting of complex sphingolipids

Complex sphingolipids form in the Golgi apparatus and require transport by vesicular carriers to reach the plasma membrane (PM) where they assemble with cholesterol to affect membrane function. The caveolin proteins have been implicated in sphingolipid trafficking but by mechanisms unknown. Here, we found that cells lacking caveolin-1 (Cav1) distributed the complex sphingolipids to the lysosome rather than to the PM. This was not seen in Cavin-1 KO cells, implicating a function for Cav1 independent of caveolae. The defect in trafficking localized to the sorting endosome where the complex sphingolipids failed to enter recycling tubules serving the PM. Sphingolipid trafficking was rescued by over-expression of Cav1, but not by a Cav1 mutant that lacked the S-palmitoylation sites. Thus, noncaveolar and palmitoylated Cav1 appears to act as a chaperone, or selectivity filter, enabling entry of the complex sphingolipids into endocytic recycling tubules to shape the composition of the PM.

cell biology↗

bioRxiv2025

Structure and function of a fungal AB toxin-like chimerolectin involved in anti-nematode defense

Fungal defense against predators largely relies on protein toxins, many of which are lectins. We previously showed that the production of the nematotoxin CCTX2 is upregulated in the Agaricomycete Coprinopsis cinerea upon predation by nematodes. Here, we classify CCTX2 as the founding member of a family of fungal chimerolectins. Cryo-EM analysis to 3.2 [A] resolution reveals five domains. The four N-terminal {beta}-trefoil fold (BTF) domains cradle a C-terminal domain, which exhibits a novel +{beta} protein fold. Mutational analysis shows that both N-terminal and C-terminal domains are required for nematotoxicity. While the biochemical function of the C-terminal domain remains unclear, the first two BTF domains enable CCTX2 to bind to glycosphingolipids with LacNAc or LacdiNAc glycoepitopes on nematode intestinal epithelial cells. Experiments in the model nematode Caenorhabditis elegans demonstrate that the chimerolectin CCTX2 exploits the endocytic and retrograde trafficking machinery of the target cell to exert its toxicity and obtain access to the yet-to-be-identified intracellular target of the non-lectin domain. The structure and mode of action of CCTX2 is reminiscent of bacterial and plant AB toxins.

microbiology↗

bioRxiv2021

Structural basis for acyl chain control over glycosphingolipid sorting and vesicular trafficking

The complex sphingolipids exhibit a diversity of ceramide acyl chain structures that influence their trafficking and intracellular distributions, but how the cell discerns among the different ceramides to affect such sorting remains unknown. To address mechanism, we synthesized a library of GM1 glycosphingolipids with naturally varied acyl chains and quantitatively assessed their sorting among different endocytic pathways. We found that a stretch of at least 14 saturated carbons extending from C1 at the water-bilayer interface dictated lysosomal sorting by exclusion from endosome sorting tubules. Sorting to the lysosome by the C14*-motif was cholesterol dependent. Perturbations of the C14*-motif by unsaturation enabled GM1 entry into endosomal sorting tubules of the recycling and retrograde pathways independently of cholesterol. Unsaturation occurring beyond the C14*-motif in very long acyl chains rescued lysosomal sorting. These results define a structural motif underlying membrane organization of sphingolipids and implicate cholesterol-sphingolipid nanodomain formation in sorting mechanisms.

cell biology↗