The LCB4 (YOR171c) and LCB5 (YLR260w) genes of Saccharomyces encode sphingoid long chain base kinases

Sphingolipid long chain bases (LCBs) and phosphorylated derivatives, particularly sphingosine l-phosphate, are putative signaling molecules. To help elucidate the physiological roles of LCB phosphates, we identified two Saccharomyces cerevisiae genes, LCB4 (YOR171c) and LCB5 (YLR260w), which encode LCB kinase activity. This conclusion is based upon the synthesis of LCB kinase activity in Escherichia coli expressing either LCB gene. LCB4 encodes most (97%) Saccharomyces LCB kinase activity, with the remainder requiring LCB5. Log phase Icb4-deleted yeast cells make no LCB phosphates, showing that the Lcb4 kinase synthesizes all detectable LCB phosphates under these growth conditions. The Lcb4 and Lcb5 proteins are paralogs with 53% amino acid identity but are not related to any known protein, thus revealing a new class of lipid kinase, Two-thirds of the Lcb4 and one-third of the Lcb5 kinase activity are in the membrane fraction of yeast cells, a puzzling finding in that neither protein contains a membrane-localization signal. Both enzymes can use phytosphingosine, dihydrosphingosine, or sphingosine as substrate. LCB4 and LCBB should be useful for probing the functions of LCB phosphates in S. cerevisiae, Potential mammalian cDNA homologs of the LCB kinase genes may prove useful in helping to understand the function of sphingosine l-phosphate in mammals.