REGULATION OF DIACYLGLYCEROL KINASE THETA

Diacylglycerol (DAG) and phosphatidic acid are important signaling molecules involved in numerous signaling pathways. The diacylglycerol kinases (DGKs) are particularly poised to regulate the cellular levels of these two lipids. Although interest in these enzymes is increasing, information regarding their regulation at a molecular level is scarce, particularly information pertaining to the enzymology of these enzymes. We recently showed that DGK‐θ behaves a “quasi‐scooter” given its sensitivity to both the bulk (total) and surface concentration of substrate. Additionally, stimulation of the cultured fibroblasts expressing this enzyme leads to an increase in the apparent K m (K mapp ) which was decreased in response to an increase in the bulk substrate (DOG, dioleylglycerol) concentration. Further progress on understanding the mammalian DGKs at a molecular level have been hindered in large part by the paucity of purified DGKs with significant catalytic activity. To this end, we have purified DGK‐θ to apparent homogeneity. Interestingly, the activity of purified DGK‐θ is extremely weak. Interestingly, addition of certain proteins results in a dramatic increase in its activity in vitro. Studies designed to characterize these activating proteins and their effects on the enzymology of DGK‐θ are in progress. One of the major challenges of this research will be to identify the physiologically relevant activating protein(s) and work is in progress to accomplish this goal.