Zinc binding drives sheet formation by the SAM domain of diacylglycerol kinase δ.

The diacylglycerol kinase (DGK) family of enzymes plays critical roles in lipid signaling pathways by converting diacylglycerol to phosphatidic acid, thereby downregulating signaling by the former and upregulating signaling by the latter second messenger. Ten DGK family isozymes have been identified to date, which possess different interaction motifs imparting distinct temporal and spatial control of DGK activity to each isozyme. Two DGK family members, delta and eta, contain a sterile alpha motif (SAM) domain. The SAM domain of DGK delta 1 forms helical polymers that are important for retaining the enzyme in cytoplasmic puncta, thereby inhibiting activity at the plasma membrane until pathway activation. Because zinc was found to be important for stabilizing the similar SAM polymers of the scaffolding protein Shank-3, we investigated the potential role of zinc in DGK delta SAM domain (DGK delta SAM) assembly. We find that DGK delta SAM binds zinc at multiple sites, driving the organization of the DGK delta SAM into large sheets of polymers. Moreover, a mutant DGK delta containing a SAM domain refractory to zinc binding diminishes the formation of cytoplasmic puncta, shows partially impaired regulation of transport to the plasma membrane, and lacks the ability to inhibit the formation or CopII coated vesicles. These results suggest that zinc may play an important role in the assembly and physiology of the DGK delta isozyme.