Disease relevance of DGUOK

• The cDNA was expressed in Escherichia coli and shown to encode a protein with the same substrate specificity as described for the mitochondrial deoxyguanosine kinase (dGK; EC 2.7.1.113) [1].
• Alignment of the dGK and herpes simplex virus type 1 thymidine kinase amino acid sequences showed that five regions, including the substrate-binding pocket and the ATP-binding glycine loop, were also conserved in dGK [1].
• In the case of TK2 deficiency, affected individuals suffer severe myopathy and, in the case of dGK deficiency, devastating liver or multi-systemic disease [2].
• Deoxycytidine kinase and deoxyguanosine kinase of Lactobacillus acidophilus R-26 are colinear products of a single gene [3].
• The pattern of deoxycytidine- and deoxyguanosine kinase activity in relation to messenger RNA expression in blood cells from untreated patients with B-cell chronic lymphocytic leukemia [4].

High impact information on DGUOK

• The main supply of deoxyribonucleotides (dNTPs) for mtDNA synthesis comes from the salvage pathway initiated by dGK and thymidine kinase-2 (TK2) [5].
• Mammals have four deoxyribonucleoside kinases, the cytoplasmic (TK1) and mitochondrial (TK2) thymidine kinases, and the deoxycytidine (dCK) and deoxyguanosine (dGK) kinases, which salvage the precursors for nucleic acids synthesis [6].
• The human deoxyguanosine kinase is highly specific for purine substrates; this is apparently due to the presence of Arg 118, which provides favorable hydrogen bonding interactions with the substrate [7].
• Our data showed that the human deoxycytidine kinase is located in the cell nucleus and the human deoxyguanosine kinase is located in the mitochondria [8].
• Northern blot analysis determined the length of dGK mRNA to 1.3 kbp with no cross-hybridization to the 2.8-kbp dCK mRNA. dGK mRNA was detected in all tissues investigated with the highest expression levels in muscle, brain, liver, and lymphoid tissues [1].

Chemical compound and disease context of DGUOK

• Three of the four deoxynucleoside kinases required for growth of Lactobacillus acidophilus R-26 exist as heterodimeric pairs specific for deoxyadenosine (dAK) and deoxycytidine (dCK) or dAK and deoxyguanosine (dGK) [3].
• Expression and purification of recombinant protein from induced Escherichia coli extracts revealed that it catalyses efficient phosphorylation of dGuo, arabinosyl guanine, dAdo, 2-chloro-2'-deoxyadenosine and dIno similar to purified dGK [9].
• Mutations in the deoxyguanosine kinase and polymerase gamma genes have been identified in hepatocerebral forms, whereas thymidine kinase 2 gene mutations have been found in patients with isolated myopathy, encephalomyopathy, or spinal muscular atrophy [10].
• A highly active form of human recombinant deoxyguanosine kinase (dGK) phosphorylated purine nucleoside analogs active against cytomegalovirus, hepatitis B virus, and human immunodeficiency virus, such as penciclovir, 2',3'-dideoxyguanosine and 3'-fluoro-2',3'-dideoxyguanosine [11].

Biological context of DGUOK

• In striking contrast to ATP, the phosphorylation reaction follows strict Michaelis-Menten kinetics, with K(m) values of 74 and 92 microM for dCK and dGK, respectively, and V(max) values 40-50% that for ATP [12].
• In conclusion, we observed a high prevalence of DGUOK mutations (17%) in patients with hepatic involvement and combined respiratory chain deficiencies with hepatic involvement [13].
• We evaluated the hypothesis that dFdC-mediated deoxyribonucleoside triphosphate perturbation enhances the phosphorylation of substrates that use deoxycytidine kinase or deoxyguanosine kinase, because these enzymes are inhibited by dCTP or dGTP, respectively [14].
• These mutations were associated with variable phenotypes, and their low frequencies suggests that dGK is not the only gene responsible for mitochondrial DNA depletion in liver [15].
• Here we describe the subcellular distribution of dGK during apoptosis in human epithelial kidney 293 cells and human lymphoblast Molt-4 cells [16].

Anatomical context of DGUOK

• However, low expression of dGK is the most apparent alteration in both resistant cell lines [17].
• Two of the four human deoxyribonucleoside kinases, deoxyguanosine kinase (dGK) and thymidine kinase-2 (TK2), are expressed in mitochondria [18].
• These results from whole-cell experiments are consistent with those from the cell-free system and strongly suggest that ara-G is phosphorylated by both kinases, and at low substrate concentrations, dGK is preferred enzyme [19].
• The redistribution of dGK from the mitochondria to the cytosol may be of importance for the activation of apoptotic purine nucleoside cofactors such as dATP and demonstrates that mitochondrial matrix proteins may selectively leak out during apoptosis [16].
• For this purpose, dCK and dGK analyses were done in blood cells from 59 untreated symptomatic patients with CLL [4].

Associations of DGUOK with chemical compounds

• Our findings suggest that dCK and dGK are evolutionarily related, as well as related to the family of herpes virus thymidine kinases [1].
• Subunits bearing three of these activities are uniquely organized into two heterodimers, deoxyadenosine/deoxycytidine kinase (dAK/dCK) and deoxyadenosine/deoxyguanosine kinase (dAK/dGK), which, along with a distinct deoxythymidine kinase (TK), catalyze the parallel first committed steps of dNTP biosynthesis [20].
• Arabinosylguanine is phosphorylated by both cytoplasmic deoxycytidine kinase and mitochondrial deoxyguanosine kinase [19].
• Only the dCK+ cell line phosphorylated 1-beta-D-arabinofuranosylcytosine (used as a substrate for dCK) in a cell-free system; phosphorylation of this compound by dGK+ was below the limit of detection [19].
• Direct enzymatic phosphorylation does not seem to be essential to the mechanism of action of the nucleoside insofar as competitive inhibition of deoxycytidine kinase (an enzyme that directly phosphorylates purines as well as pyrimidines) or of deoxyguanosine kinase fails to inhibit 8BrGuo stimulation selectively [21].

Other interactions of DGUOK

• The analogue 1-(2-deoxy-beta-D-ribofuranosyl)-7-iodoisocarbostyril (EN2) showed poor relative-phosphorylation efficiencies (kcat/Km) with both TK1 and dGK, but not with TK2 [22].
• We assume that dCK activation elicited by cellular damage might be a proapoptotic factor in terms of generating dATP well before the release of cytochrome c and deoxyguanosine kinase from mitochondria [23].
• Each affected child was homozygous for the novel DGUOK p.D255Y mutation, but had no CTH mutation, indicating that the hepatocerebral form of MDS might be associated with secondary cystathioninuria [24].
• One mutant that lacked deoxycytidine kinase activity, designated CEM/ara-C, retained about 10% of wild-type deoxyadenosine kinase and deoxyguanosine kinase activity each but maintained normal adenosine kinase or thymidine kinase activity [25].
• The mRNA expression for dCK, dGK and 5'-NT (expressed as the ratio of the respective gene and the reference gene) in pediatric ALL and AML patients showed a large interindividual variability from 0.06 to 2.34, non-detectable to 0.06 and 0.04 to 0.30, respectively [26].

Analytical, diagnostic and therapeutic context of DGUOK

• Western-blot analysis did not detect dGK protein in the liver of affected individuals [5].
• Site-directed mutagenesis was used to introduce the mutations detected in patients A and B into the TK2 and dGK cDNAs, respectively [2].
• Real-time quantitative PCR assays for deoxycytidine kinase, deoxyguanosine kinase and 5'-nucleotidase mRNA measurement in cell lines and in patients with leukemia [26].
• These results show that the quantitative evaluation by RQ-PCR is a valuable tool in the determination of dCK, dGK and 5'-NT mRNA levels in cell lines and in clinical samples which were expressed at various levels [26].
• In the case of dGK, the determinations were carried out with both an immunoblotting assay and selective enzyme activity measurements [27].

References