Daniel Raben Ph. D.
Biochemistry and chemistry of lipids and lipid metabolizing enzymes involved in signaling cascades
A major effort in our laboratory is focused on understanding the biochemistry and chemistry underlying the molecular aspects involved in regulating lipid metabolizing signaling enzymes and the physiological roles of this regulation. Control of lipid metabolizing enzymes involves the modulation of two key parameters; their sub-cellular distribution and their intrinsic enzymatic activity. Our studies have concentrated on three families of lipid-metabolizing signaling enzymes: diacylglycerol kinases, phospholipases D, and phospholipases C.
Specific Areas of Interest
Interfacial Enzymology of Lipid Metabolizing Signaling Enzymes: We are particularly interested in identifying the critical modulating proteins, lipids, and post-translational modifications that alter the localization and/or activity of lipid metabolizing enzymes. In these studies we consider the fact that these enzymes act as interfacial enzymes and their regulation includes a number of interfacial-dependent parameters. Our recent studies have identified some of the diacylglycerol metabolizing enzyme DGK-θ (diacylglycerol kinase-theta) interfacial parameters that are altered upon neuronal depolarization. Further, our studies demonstrated that activation of DGK-θ requires a protein that contains a polybasic region. We have recently obtained evidence that identifies at least one, if not only, activator binding domain on DGK-θ.
Enzyme Structure/Function Studies: We are also interested in the structural components of these enzymes that are critical for their distribution/re-distribution to specific sub-cellular compartments. Additionally, and to compliment the enzymology studies, we are interested in elucidating the catalytic mechanism(s) of these enzymes. These studies will be conducted partly in collaboration with Dr. Mario Amzel. Our long-term goal is to understand the biochemistry and chemistry of these enzymes and determine how changes in their sub-cellular localization and/or enzymatic activity affect their signaling functions.
Physiological Functions of DGKs in Neurons: There is growing evidence that DGKs play physiological roles in mammalian neurons. This evidence includes cellular localization of specific isoforms, and the observations that likely modulate (a) susceptibility to epileptic seizures (DGK-ε), (b) neuronal spine density (DGK-ζ and DGK-β), and (c) pre-synaptic glutamate release during DHPG (3,5-dihydroxyphenylglycine)-induced long-term potentiation (DGK-ι). We are currently examining the role of DGK-θ in glutamatergic neurons. These studies have initially focused on identifying the physiologic regulator of DGK-θ, and test the hypothesis that this enzyme modulates induced glutamate release in these mammalian neurons. We discovered that DGK-θ modulates glutamate release from cortical and hippocampal neurons in part by modulating synaptic vesicle cycling. These studies are conducted in collaboration with Dr. Rick Huganier’s laboratory.