Cis-unsaturated sphingolipids support growth of sphingoid base-deficient yeast but impair plasma membrane integrity

Sphingoid long-chain bases (LCBs) form the backbone of sphingolipids, and their structures vary among eukaryotes. For example, in budding yeast, phytosphingosine is the major LCB, while animals primarily use sphingosine. Animals and plants also produce structurally diverse LCBs, including species with additional cis or trans double bonds, which are absent in yeast. Here, we show that yeast can grow even when its endogenous LCBs are replaced with plant-type unsaturated forms, such as (8Z)-4-hydroxy-8-sphingenine or (4E,8E)-sphinga-4,8-dienine. These cells synthesized ceramides and complex sphingolipids, indicating efficient incorporation of the exogenous LCBs into sphingolipid metabolism. However, cells harboring these unsaturated LCBs exhibited abnormalities in plasma membrane permeability, lipid order, and distribution of some plasma membrane-localized proteins. In contrast, these cells reinforce their cell walls, presumably to compensate for the impaired plasma membrane integrity. Notably, to our knowledge, this is the first report of eukaryotic cells whose sphingolipids are composed almost exclusively of LCBs with a cis double bond, providing a unique model platform to investigate how LCB structural features influence membrane function.