The DAG-kinase catalytic domain or DAGKc domain is present in mammalian lipid kinases, such as diacylglycerol (DAG), ceramide and sphingosine kinases, as well as in related bacterial proteins [1,2]. Eukaryotic DAG-kinase (EC 2.7.1.107) catalyzes the phosphorylation of DAG to phosphatidic acid, thus modulating the balance between the two signaling lipids. At least ten different isoforms have been identified in mammals, which form 5 groups characterized by different functional domains, such as the calcium-binding EF hand (see <PDOC00018>), PH (see <PDOC50003>), SAM (see <PDOC50105>), DAG/PE-binding C1 domain (see <PDOC00379>) and ankyrin repeats (see <PDOC50088>) [3].

In bacteria, an integral membrane DAG kinase forms a homotrimeric protein that lacks the DAGKc domain (see <PDOC00820>). In contrast, the bacterial yegS protein is a soluble cytosolic protein that contains the DAGKc domain in the N-terminal part. YegS is a lipid kinase with two structural domains, wherein the active site is located in the interdomain cleft, C-terminal to the DAGKc domain which forms an α/β fold (see <PDB: 2BON; A>) [2]. The tertiary structure resembles that of NAD kinases and contains a metal-binding site in the C-terminal region [2,4].

Some proteins known to contain a DAGKc domain are listed below:

• Mammalian diacylglycerol kinase (DGK/DAGK, EC 2.7.1.107), which upon cell stimulation converts the second messenger DAG into phosphatidate, initiating the resynthesis of phosphatidylinositols and attenuating protein kinase C activity.
• Mammalian sphingosine kinase (EC 2.7.1.91), which catalyzes the phosphorylation of sphingosine to form sphingosine 1-phosphate (SPP), a lipid mediator with both intra- and extracellular functions.
• Mammalian mitochondrial acylglycerol kinase (mulK, EC 2.7.1.94), a lipid kinase that can phosphorylate both monoacylglycerol and diacylglycerol to form lysophosphatidic acid and phosphatidic acid, respectively.
• Mammalian ceramide kinase (EC 2.7.1.138), which catalyzes specifically the phosphorylation of ceramide to form ceramide 1-phosphate.
• Bacterial lipid kinase yegS (EC 2.7.1.-), which in vitro phosphorylates phosphatidylglycerol but not diacylglycerol; probably phosphorylates lipids.
• Fruit fly diacylglycerol kinases (EC 2.7.1.107).
• Caenorhabditis elegans putative diacylglycerol kinase K06A1.6 and protein F52C9.3
• Plant sphingoid long-chain bases kinase.
• Yeast sphingoid long-chain bases kinase.

The profile we developed covers the entire DAGKc domain.