Mouse sphingosine kinase isoforms SPHK1a and SPHK1b differ in enzymatic traits including stability, localization, modification, and oligomerization.

J Biol Chem 2006 Feb 20;281(7):4532-9. Epub 2005 Dec 20.

Department of Biomembrane and Biofunctional Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.

Sphingosine kinases catalyze the production of the bioactive lipid molecule sphingosine 1-phosphate. Mice have two isoforms of sphingosine kinase type 1, SPHK1a and SPHK1b. In addition to the previously reported difference in their enzyme activities, we have found that these isoforms differ in several enzymatic characteristics. First, SPHK1b is unstable, whereas SPHK1a is highly stable. Degradation of SPHK1b occurs at the membrane and is inhibited by a proteasome inhibitor. Second, only SPHK1b exhibits abnormal mobility on SDS-PAGE, probably due to its SDS-resistant structure. Third, SPHK1a and SPHK1b are predominantly detected in the soluble and membrane fractions, respectively, when their degradation is inhibited. Fourth, only SPHK1b is modified with lipid, on its unique Cys residues (Cys-4 and Cys-5). Site-directed mutagenesis at these Cys residues resulted in increased sphingosine kinase activity, suggesting that the modification is inhibitory to the enzyme. Finally, SPHK1b tends to form homo-oligomers, whereas most SPHK1a is presented as monomers. We have also determined that the lipid modification of SPHK1b is involved in its homo-oligomerization. Thus, although these two proteins differ only in a few N-terminal amino acid residues, their enzymatic traits are extremely different.

Download full-text PDF

Source
http://dx.doi.org/10.1074/jbc.M510308200DOI Listing
February 2006
1 Read

Publication Analysis

Top Keywords

sphk1a sphk1b
12
sphingosine kinase
12
sphk1b
9
differ enzymatic
8
enzymatic traits
8
cys residues
8
sphk1a
5
sphk1a presented
4
second sphk1b
4
presented monomers
4
proteasome inhibitor
4
inhibitor second
4
homo-oligomers sphk1a
4
mobility sds-page
4
sds-page sds-resistant
4
sphk1b form
4
form homo-oligomers
4
abnormal mobility
4
exhibits abnormal
4
inhibited proteasome
4

Similar Publications