A ferredoxin from the thermohalophilic bacterium Rhodothermus marinus

The substrate specificity of human sphingosine kinase was investigated using a bacterially expressed poly(His)-tagged protein. Only the D-erythro isomer of the sphingoid bases, sphinganine and sphingenine, was effectively phosphorylated. Long chain 1-alkanols, alkane-1,2-diols, 2-amino-1-alkanol or 1-amino-2-alkanol and short chain 2-amino-1,3-alkanediols were very poor substrates, indicating that the kinase is recognizing the chain length and the position of the amino and secondary hydroxy group. A free hydroxy group at carbon 3 is not a prerequisite, however, since 1-O-hexadecyl-2-desoxy-2-amino-sn-glycerol was an efficient substrate with an apparent K(m) value of 3.8 microM (versus 15.7 microM for sphingenine). This finding opens new perspectives to design sphingosine kinase inhibitors. It also calls for some caution since it cannot be excluded that this ether lipid analogue is formed from precursors that are frequently used in research on platelet activating factor or from phospholipid analogues which are less prone to degradation.