Identification and characterization of yeast and human glycosphingolipid flippases
Lipid transport is an essential process with manifest importance to human health and disease. Phospholipid flippases (P4-ATPases) transport lipids across the membrane bilayer, and are involved in signal transduction, cell division, and vesicular transport. Mutations in flippase genes cause or contribute to a host of diseases such as cholestasis, neurological deficits, immunological dysfunction, and metabolic disease. Genome-wide association studies have shown that ATP10A and ATP10D variants are associated with an increased risk of diabetes, obesity, myocardial infarction, and atherosclerosis; and ATP10D SNPs are associated with elevated levels of glucosylceramide (GlcCer) in plasma from diverse European populations. Although sphingolipids are strong contributors to metabolic disease, little is known about how GlcCer is transported across cell membranes. We have identified an evolutionarily conserved clade of P4-ATPases from Saccharomyces cerevisiae (Dnf1, Dnf2), Schizosaccharomyces pombe (Dnf2), and Homo sapiens (ATP10A, ATP10D) that transport GlcCer. Further, we establish the structural determinants necessary for the specific recognition of this sphingolipid substrate. Our molecular observations clarify the relationship between these flippases and human disease, and have fundamental implications for membrane organization and sphingolipid homeostasis.