Alternative titles; symbols
HGNC Approved Gene Symbol: DGKA
Cytogenetic location: 12q13.2 Genomic coordinates (GRCh38): 12:55,927,316-55,954,023 (from NCBI)
Diacylglycerol (DAG) kinases (DGKs or DAGKs; EC 2.7.1.107), such as DGKA, phosphorylate DAG to phosphatidic acid, thus removing DAG. Phosphatidic acid functions both in signaling and phospholipid synthesis. In intracellular signaling pathways, DAGK can be viewed as a modulator that competes with protein kinase C (PKC; see 600448) for the second messenger DAG (review by Topham and Prescott, 1999).
By sequencing tryptic peptides of DG kinase purified from human white blood cells, followed by PCR of human Jurkat leukemic T cells and screening human DND41 leukemic T cells, Schaap et al. (1990) obtained full-length DAGK cDNA. The deduced 735-amino acid protein has a calculated molecular mass of 82.7 kD. It has 2 EF-hand motifs predicted to bind calcium, 2 cysteine-repeat regions, 2 putative ATP-binding sites, and a C-terminal stretch of 110 amino acids that is fully conserved between human and pig DAGK. One of the ATP-binding sites is contained within the first cysteine-rich region. Northern blot analysis detected a 3.2-kb DAGK transcript in Jurkat cells and in normal human T cells. Purified human DAGK had an apparent molecular mass of 86 kD by SDS-PAGE and 87 kD by gel filtration.
Schaap et al. (1990) found that DAGK purified from human white blood cells showed optimal activity in the presence of phosphatidylserine and deoxycholate. It showed relatively broad specificity, and DAG analogs containing an unsaturated fatty acid at the sn-2 position gave optimal enzymatic activity in the presence or absence of deoxycholate. Activity was not altered by calcium or calcium chelation. COS-7 cells overexpressing human DAGK showed 6- to 7-fold higher DAGK activity than controls.
Several mammalian isozymes of DAGK have been identified. The isoform described by Schaap et al. (1990) has been designated DGK-alpha or DAGK1. Topham and Prescott (1999) stated that all DGKs have a conserved catalytic domain and at least 2 cysteine-rich regions homologous to the C1A and C1B motifs of PKCs. Most DGKs have structural motifs that are likely to play regulatory roles, and these motifs form the basis for dividing the DGKs into 5 subtypes. Type I DGKs, such as DGK-alpha, -beta (604070), and -gamma (601854), have calcium-binding EF-hand motifs at their N termini. DGK-delta (601826) and DKG-eta (604071) contain N-terminal pleckstrin homology (PH) domains and are defined as type II. DGK-epsilon (601440) contains no identifiable regulatory domains and is a type III DGK. The defining characteristic of type IV isozymes, such as DGK-zeta (601441) and -iota (604072), is that they have C-terminal ankyrin repeats. Group V is exemplified by DGK-theta (601207), which contains 3 cysteine-rich domains and a PH domain.
Pilz et al. (1995) pointed to the growing evidence to support some form of light-activated phosphoinositide signal transduction pathway in the mammalian retina. Although this pathway had no obvious role in mammalian phototransduction, mutations in this pathway were known to cause retinal degeneration in Drosophila. For example, the 'retinal degeneration A' mutant in Drosophila is caused by an alteration in the eye-specific DAGK gene.
To maintain cellular homeostasis, intracellular DAG levels must be tightly regulated. DAG functions in intracellular signaling pathways as an allosteric activator of PKC. In addition, DAG appears to play a role in regulating RAS (see 190020) and RHO (see 165370) family proteins by activating the guanine nucleotide exchange factors VAV (164875) and RASGRP1 (603962). DAG also occupies a central position in the synthesis of major phospholipids and triacylglycerols. Topham and Prescott (1999) summarized the roles of mammalian DAGKs.
Seven-transmembrane receptor signaling is transduced by second messengers such as DAG generated in response to the heterotrimeric guanine nucleotide-binding protein G(q) (600998) and is terminated by receptor desensitization and degradation of the second messengers. Nelson et al. (2007) showed that beta-arrestins (see 107940) coordinate both processes for the G(q)-coupled M1 muscarinic receptor (CHRM1; 118510). Beta-arrestins physically interact with diacylglycerol kinases, enzymes that degrade DAG. Moreover, beta-arrestins are essential for conversion of DAG to phosphatidic acid after agonist stimulation, and this activity requires recruitment of the beta-arrestin-DGK complex to activated 7-transmembrane receptors. The dual function of beta-arrestins, limiting production of diacylglycerol (by receptor desensitization) while enhancing its rate of degradation, is analogous to their ability to recruit adenosine 3-prime,5-prime-monophosphate phosphodiesterases to G(s) (139320)-coupled beta-2-adrenergic receptors (ADRB2; 109690). Thus, Nelson et al. (2007) concluded that beta-arrestins can serve similar regulatory functions for disparate classes of 7-transmembrane receptors through structurally dissimilar enzymes that degrade chemically distinct second messengers.
Solution Structure
Van Horn et al. (2009) solved the solution structure of prokaryotic Dagk solubilized in dodecylphosphocholine micelles. The 121-amino acid Dagk subunits formed homotrimers in solution, and each subunit contributed 3 transmembrane helices to the holoenzyme. The structure suggested domain swapping between Dagk monomers, where transmembrane helix 3 of each subunit interacted with transmembrane helices 1 and 2 from an adjacent subunit, stabilizing the structure.
Crystal Structure
Li et al. (2013) presented the crystal structure for 3 functional forms of the 121-amino acid prokaryotic diacylglycerol kinase subunit, one of which was wildtype. The structure revealed a homotrimeric enzyme with 3 transmembrane helices and an amino-terminal amphiphilic helix per monomer. Bound lipid substrate and docked ATP identified the putative active site that is of the composite, shared site type. The crystal structures rationalized extensive biochemical and biophysical data on the enzyme. They were, however, at variance with the solution NMR model of van Horn et al. (2009) in that domain swapping, a key feature of the solution form, was not observed in the crystal structures.
In an effort to consider genes mutated in Drosophila as candidates for mammalian eye disease, Pilz et al. (1995) determined the map position of 3 DAGK genes in the mouse. They localized the mouse homolog of DAGK1 to chromosome 10 by linkage analysis.
By Southern blot analysis of human-hamster somatic cell hybrid DNA, Hart et al. (1994) assigned the DAGK gene to chromosome 12. Hart et al. (1994) further localized the gene to 12q13.3 by fluorescence in situ hybridization.
Hart, T. C., Champagne, C., Zhou, J., Van Dyke, T. E. Assignment of the gene for diacylglycerol kinase (DAGK) to human chromosome 12. Mammalian Genome 5: 123-124, 1994. [PubMed: 8180475] [Full Text: https://doi.org/10.1007/BF00292343]
Hart, T. C., Zhou, J., Champagne, C., Van Dyke, T. E., Rao, P. N., Pettenati, M. J. Assignment of the human diacylglycerol kinase gene (DAGK) to 12q13.3 using fluorescence in situ hybridization analysis. Genomics 22: 246-247, 1994. [PubMed: 7959783] [Full Text: https://doi.org/10.1006/geno.1994.1376]
Li, D., Lyons, J. A., Pye, V. E., Vogeley, L., Aragao, D., Kenyohn, C. P., Shah, S. T. A., Doherty, C., Aherne, M., Caffrey, M. Crystal structure of the integral membrane diacylglycerol kinase. Nature 497: 521-524, 2013. [PubMed: 23676677] [Full Text: https://doi.org/10.1038/nature12179]
Nelson, C. D., Perry, S. J., Regier, D. S., Prescott, S. M., Topham, M. K., Lefkowitz, R. J. Targeting of diacylglycerol degradation to M1 muscarinic receptors by beta-arrestins. Science 315: 663-666, 2007. [PubMed: 17272726] [Full Text: https://doi.org/10.1126/science.1134562]
Pilz, A., Schaap, D., Hunt, D., Fitzgibbon, J. Chromosomal localization of three mouse diacylglycerol kinase (DAGK) genes: genes sharing sequence homology to the Drosophila retinal degeneration A (rdgA) gene. Genomics 26: 599-601, 1995. [PubMed: 7607687] [Full Text: https://doi.org/10.1016/0888-7543(95)80182-l]
Schaap, D., de Widt, J., van der Wal, J., Vandekerckhove, J., van Damme, J., Gussow, D., Ploegh, H. L., van Blitterswijk, W. J., van der Bend, R. L. Purification, cDNA-cloning and expression of human diacylglycerol kinase. FEBS Lett. 275: 151-158, 1990. [PubMed: 2175712] [Full Text: https://doi.org/10.1016/0014-5793(90)81461-v]
Topham, M. K., Prescott, S. M. Mammalian diacylglycerol kinases, a family of lipid kinases with signaling functions. J. Biol. Chem. 274: 11447-11450, 1999. [PubMed: 10206945] [Full Text: https://doi.org/10.1074/jbc.274.17.11447]
Van Horn, W. D., Kim, H.-J., Ellis, C. D., Hadziselimovic, A., Sulistijo, E. S., Karra, M. D., Tian, C., Sonnichsen, F. D., Sanders, C. R. Solution nuclear magnetic resonance structure of membrane-integral diacylglycerol kinase. Science 324: 1726-1729, 2009. [PubMed: 19556511] [Full Text: https://doi.org/10.1126/science.1171716]