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Cloning and expression of human mitochondrial deoxyguanosine kinase cDNA
L Wang1, U Hellman, S Eriksson
1Department of Veterinary Medical Chemistry, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Abstract:
Mammalian mitochondrial deoxyguanosine kinase (dGK) is responsible for phosphorylation of purine deoxyribonucleosides in the mitochondrial matrix. Using a RT-PCR-generated probe, based on amino acid sequence information from proteolytic fragments of purified bovine dGK, we have cloned a cDNA from a human brain cDNA library that encodes a 30 kDa protein. The deduced amino acid sequence of this protein included the sequence of all six peptides isolated and sequenced from purified dGK. 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. Northern blot analysis demonstrated one dominant positive mRNA of 1.35 kb and it was found in several tissues at similar levels. The coding sequence of dGK showed 46% identity to the coding sequence of cytosolic deoxycytidine kinase, and conserved sequence motifs among the known deoxynucleoside kinase were identified.
Insights
Researchers identified the human mitochondrial deoxyguanosine kinase (dGK), crucial for purine deoxyribonucleoside phosphorylation. This enzyme efficiently phosphorylates various nucleosides, similar to purified dGK, and is expressed across multiple tissues.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Mitochondrial deoxyguanosine kinase (dGK) plays a vital role in phosphorylating purine deoxyribonucleosides within the mitochondrial matrix.
- Understanding the precise molecular identity and function of dGK is essential for comprehending mitochondrial purine metabolism.
Purpose of the Study:
- To clone and characterize the human mitochondrial deoxyguanosine kinase (dGK).
- To confirm the enzymatic activity and tissue expression pattern of the cloned dGK.
Main Methods:
- Utilized RT-PCR with a probe derived from bovine dGK amino acid sequences to screen a human brain cDNA library.
- Expressed and purified recombinant protein in Escherichia coli for enzymatic assays.
- Performed Northern blot analysis to determine mRNA expression levels and size.
Main Results:
- Successfully cloned a human cDNA encoding a 30 kDa protein, matching the deduced amino acid sequence of purified dGK.
- Recombinant dGK demonstrated efficient phosphorylation of dGuo, arabinosyl guanine, dAdo, 2-chloro-2'-deoxyadenosine, and dIno.
- Northern blot revealed a dominant 1.35 kb mRNA transcript expressed at similar levels in various human tissues.
Conclusions:
- The cloned cDNA represents the human mitochondrial deoxyguanosine kinase (dGK).
- The characterized dGK enzyme exhibits broad substrate specificity and consistent tissue expression.
- Identified conserved sequence motifs suggest evolutionary relationships with other deoxynucleoside kinases.