Post-translational regulation of phosphatidylglycerolphosphate synthase in response to inositol.

Phosphatidylglycerolphosphate synthase (Pgs1p) catalyses the committed step in the synthesis of cardiolipin (CL). This is the only step of CL synthesis that is regulated by inositol. We have shown previously that Pgs1p enzyme activity is decreased within minutes after supplementation with inositol, but PGS1 expression is unaltered. We utilized an epitope-tagged Pgs1p to determine if the rapid decrease in activity following inositol was because of degradation or inactivation of the protein. In this report, we show that, in response to inositol, the decrease in CL content and Pgs1p enzyme activity are associated with increased phosphorylation of Pgs1p, but not with degradation or mislocalization of the protein. This is the first evidence of phosphorylation of a phospholipid biosynthetic enzyme in response to inositol and identifies a new mechanism of inositol-mediated regulation.