The entry includes Drosophila protein spinster [], its vertebrate homologues, and the MFS-type efflux pumps from bacteria. Humans contain three homologues called protein spinster homologues 1 (SPNS1), 2 (SPNS2), and 3 (SPNS3). Protein spinster and its homologues may be sphingolipid transporters that play central roles in endosomes and/or lysosomes storage. SPNS2 is also called sphingosine 1-phosphate (S1P) transporter and is required for migration of myocardial precursors. S1P is a secreted lipid mediator that plays critical roles in cardiovascular, immunological, and neural development and function [, , ]. These proteins belong to the Major Facilitator Superfamily (MFS) of membrane transport proteins, which are thought to function through a single substrate binding site, alternating-access mechanism involving a rocker-switch type of movement. Also included in this family are the probable sphingolipid transporter spinster homologues 1-3 from Arabidopsis thaliana.
