ABSTRACT
DNA methylation of cytosine in eukaryotic cells is a common epigenetic modification, which plays an important role in gene expression and thus affects various cellular processes like development and carcinogenesis. The occurrence of 5-methyl-2'-deoxycytosine (5mC) as well as the distribution pattern of this epigenetic marker were shown to be crucial for gene regulation and can serve as important biomarkers for diagnostics. DNA polymerases distinguish little, if any, between incorporation opposite C and 5mC, which is not surprising since the site of methylation is not involved in Watson-Crick recognition. Here, we describe the development of a DNA polymerase variant that incorporates the canonical 2'-deoxyguanosine 5'-monophosphate (dGMP) opposite C with higher efficiency compared to 5mC. The variant of Thermococcus kodakaraensis (KOD) exo- DNA polymerase was discovered by screening mutant libraries that were built by rational design. We discovered that an amino acid substitution at a single site that does not directly interact with the templating nucleobase, may alter the ability of the DNA polymerase in processing C in comparison to 5mC. Employing these findings in combination with a nucleotide, which is fluorescently labeled at the terminal phosphate, indicates the potential use of the mutant DNA polymerase in the detection of 5mC.
Subject(s)
5-Methylcytosine/pharmacology , DNA Methylation/drug effects , DNA-Directed DNA Polymerase/genetics , DNA-Directed DNA Polymerase/metabolism , Thermococcus/enzymology , Thermococcus/genetics , 5-Methylcytosine/chemistry , DNA, Bacterial/chemistry , DNA, Bacterial/genetics , DNA-Directed DNA Polymerase/chemistry , Epigenesis, Genetic , Models, Molecular , Molecular Conformation , MutationABSTRACT
Gene expression is extensively regulated by the occurrence and distribution of the epigenetic marker 2'-deoxy 5-methylcytosine (5mC) in genomic DNA. Because of its effects on tumorigenesis there is an important link to human health. In addition, detection of 5mC can serve as an outstanding biomarker for diagnostics as well as for disease therapy. Our previous studies have already shown that, by processing O(6) -alkylated 2'-deoxyguanosine triphosphate (dGTP) analogues, DNA polymerases are able to sense the presence of a single 5mC unit in a template. Here we present the synthesis and evaluation of an extended toolbox of 6-substituted 2-aminopurine-2'-deoxyribonucleoside 5'-triphosphates modified at positionâ 6 with various functionalities. We found that sensing of 5-methylation by this class of nucleotides is more general, not being restricted to O(6) -alkyl modification of dGTP but also applying to other functionalities.
Subject(s)
Cytosine/metabolism , Purine Nucleotides/chemistry , Cytosine/chemistry , Methylation , Purine Nucleotides/chemical synthesis , Purine Nucleotides/metabolismABSTRACT
5-Methyl-2'-deoxycytosine, the most common epigenetic marker of DNA in eukaryotic cells, plays a key role in gene regulation and affects various cellular processes such as development and carcinogenesis. Therefore, the detection of 5mC can serve as an important biomarker for diagnostics. Here we describe that modified dGTP analogues as well as modified primers are able to sense the presence or absence of a single methylation of C, even though this modification does not interfere directly with Watson-Crick nucleobase pairing. By screening several modified nucleotide scaffolds, O(6)-modified 2'-deoxyguanosine analogues were identified as discriminating between C and 5mC. These modified nucleotides might find application in site-specific 5mC detection, for example, through real-time PCR approaches.
