Diacylglycerol kinase


Diacylglycerol kinase is a family of enzymes that catalyzes the conversion of diacylglycerol to phosphatidic acid, utilizing ATP as a source of the phosphate. In non-stimulated cells, DGK activity is low, allowing DAG to be used for glycerophospholipid biosynthesis, but on receptor activation of the phosphoinositide pathway, DGK activity increases, driving the conversion of DAG to PA. As both lipids are thought to function as bioactive lipid signaling molecules with distinct cellular targets, DGK therefore occupies an important position, effectively serving as a switch by terminating the signalling of one lipid while simultaneously activating signalling by another.
In bacteria, DGK is very small membrane protein which seems to contain three transmembrane domains. The best conserved region is a stretch of 12 residues which are located in a cytoplasmic loop between the second and third transmembrane domains. Some Gram-positive bacteria also encode a soluble diacylglycerol kinase capable of reintroducing DAG into the phospholipid biosynthesis pathway. DAG accumulates in Gram-positive bacteria as a result of the transfer of glycerol-1-phosphate moieties from phosphatidylglycerol to lipotechoic acid.

Mammalian DGK Isoforms

Currently, nine members of the DGK family have been cloned and identified. Although all family members have conserved catalytic domains and two cysteine rich domains, they are further classified into five groups according to the presence of additional functional domains and substrate specificity. These are as follows:
Mutations in the genes for deoxyguanosine kinase along with myophosphorylase have been associated with muscle glycogenosis and mitochondrial hepatopathy. The duplication in exon 6 of dGK that results in a truncated protein and the G456A PYGM mutation have been associated with phosphorylase deficiency in muscle, cytochrome c oxidase deficiency in liver, severe congenital hypotonia, hepatomegaly, and liver failure. This expands on the current understanding of McArdle disease and suggests that this combination of mutations could result in a complex disease with severe phenotypes.