ER residency of the ceramide phosphoethanolamine synthase SMSr relies on homotypic oligomerization mediated by its SAM domain

Cabukusta, Birol; Kol, Matthijs; Kneller, Laura; Hilderink, Angelika; Bickert, Andreas; Mina, John G.M.; Korneev, Sergei; Holthuis, Joost C.M.

Abstract

SMSr/SAMD8 is an ER-resident ceramide phosphoethanolamine synthase with a critical role in controlling ER ceramides and suppressing ceramide-induced apoptosis in cultured cells. SMSr-mediated ceramide homeostasis relies on the enzyme’s catalytic activity as well as on its N-terminal sterile α-motif or SAM domain. Here we report that SMSr-SAM is structurally and functionally related to the SAM domain of diacylglycerol kinase DGKδ, a central regulator of lipid signaling at the plasma membrane. Native gel electrophoresis indicates that both SAM domains form homotypic oligomers. Chemical crosslinking studies show that SMSr self-associates into ER-resident trimers and hexamers that resemble the helical oligomers formed by DGKδ-SAM. Residues critical for DGKδ-SAM oligomerization are conserved in SMSr-SAM and their substitution causes a dissociation of SMSr oligomers as well as a partial redistribution of the enzyme to the Golgi. Conversely, treatment of cells with curcumin, a drug disrupting ceramide and Ca2+ homeostasis in the ER, stabilizes SMSr oligomers and promotes retention of the enzyme in the ER. Our data provide first demonstration of a multi-pass membrane protein that undergoes homotypic oligomerization via its SAM domain and indicate that SAM-mediated self-assembly of SMSr is required for efficient retention of the enzyme in the ER.

Citation

Cabukusta, B., Kol, M., Kneller, L., Hilderink, A., Bickert, A., Mina, J. G., …Holthuis, J. C. (2017). ER residency of the ceramide phosphoethanolamine synthase SMSr relies on homotypic oligomerization mediated by its SAM domain. Scientific Reports, 7, Article 41290. https://doi.org/10.1038/srep41290

• Journal Article Type: Article
• Acceptance Date: Dec 19, 2016
• Online Publication Date: Jan 25, 2017
• Publication Date: Jan 25, 2017
• Deposit Date: Oct 17, 2017
• Publicly Available Date: Oct 18, 2017
• Journal: Scientific Reports
• Publisher: Nature Research
• Peer Reviewed: Peer Reviewed
• Volume: 7
• Article Number: 41290
• DOI: https://doi.org/10.1038/srep41290