Cfs1p, a Novel Membrane Protein in the PQ-Loop Family, Is Involved in Phospholipid Flippase Functions in Yeast

摘要

Type 4 P-type ATPases (P4-ATPases) function as phospholipid flippases, which translocate phospholipids from the exoplasmic leaflet to the cytoplasmic leaflet of the lipid bilayer, to generate and maintain asymmetric distribution of phospholipids at the plasma membrane and endosomal/Golgi membranes. The budding yeast Saccharomyces cerevisiae has four heteromeric flippases ([Drs2p][1], [Dnf1p][2], [Dnf2p][3], and [Dnf3p][4]), associated with the [Cdc50p][5] family noncatalytic subunit, and one monomeric flippase, [Neo1p][6]. They have been suggested to function in vesicle formation in membrane trafficking pathways, but details of their mechanisms remain to be clarified. Here, to search for novel factors that functionally interact with flippases, we screened transposon insertional mutants for strains that suppressed the cold-sensitive growth defect in the [cdc50][5] Δ mutant. We identified a mutation of [YMR010W][7] encoding a novel conserved membrane protein that belongs to the PQ-loop family including the cystine transporter cystinosin and the SWEET sugar transporters. We named this gene [CFS1][7] ( cdc fifty suppressor 1). GFP-tagged [Cfs1p][7] was partially colocalized with [Drs2p][1] and [Neo1p][6] to endosomal/late Golgi membranes. Interestingly, the [cfs1][7] Δ mutation suppressed growth defects in all flippase mutants. Accordingly, defects in membrane trafficking in the flippase mutants were also suppressed. These results suggest that [Cfs1p][7] and flippases function antagonistically in membrane trafficking pathways. A growth assay to assess sensitivity to duramycin, a phosphatidylethanolamine (PE)-binding peptide, suggested that the [cfs1][7] Δ mutation changed PE asymmetry in the plasma membrane. [Cfs1p][7] may thus be a novel regulator of phospholipid asymmetry. [1]: http://www.yeastgenome.org/locus/S000000024/overview [2]: http://www.yeastgenome.org/locus/S000000968/overview [3]: http://www.yeastgenome.org/locus/S000002500/overview [4]: http://www.yeastgenome.org/locus/S000004772/overview [5]: http://www.yeastgenome.org/locus/S000000690/overview [6]: http://www.yeastgenome.org/locus/S000001310/overview [7]: http://www.yeastgenome.org/locus/S000004612/overview