BPS2026 – Constitutive plasma membrane raft formation in Saccharomyces cerevisiae and other fungi

Ordered lipid domain (raft) formation and properties in fungal plasma membranes are poorly understood relative to that of rafts in fungal vacuoles. Using a FRET assay, we measured the formation and thermal stability of plasma membrane S. cerevisiae rafts in vivo as well as raft formation in isolated plasma membranes. Ordered lipid domain formation was detected both in vivo and isolated plasma membrane, with similar properties as those in vacuoles. In intact cells, a thermal transition occurred with a midpoint of about 45 ± 1.0°C. As in the case of vacuoles, in vivo plasma membrane rafts were slightly less thermally stable when S. cerevisiae cultures were grown at 20°C rather than the control condition of 30°C. However, unlike vacuoles, rafts were detected in both exponential and stationary growth phase. Several S. cerevisiae strains with mutations in sphingolipid or ergosterol synthesis showed minimal effects on raft formation, with the exception of elo3Δ , a sphingolipid acyl chain elongase mutant. Rafts in isolated S. cerevisiae plasma membranes were more thermally stable than those in mammalian plasma membranes, and unlike mammalian plasma membranes, abolishing lipid asymmetry through solubilization and reconstitution of S. cerevisiae plasma membranes did not induce further raft stability. FRET also detected raft formation in Candida albicans and Cryptococcus neoformans . The constitutive presence of ordered lipid domains may be a general feature of fungal plasma membranes.