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DNA polymerase that catalyzes the polymerization of deoxyribonucleotides to form DNA can be influenced by cation-cofactors. In RNA viruses, like HIV, reverse transcriptase uses Mg2+ ions as a cofactor to perform catalysis. Reverse transcriptase is an enzyme that catalyzes DNA synthesis using the information available in the mRNA, i.e. reverse transcription. However, a new study reveals that this enzyme, reverse transcriptase can also be influenced by some cations like Mn2+, Co2+, and Zn2+. In fact, these cations can act as a cofactor for the enzyme reverse transcriptase. Though Zn2+ supports DNA synthesis, it can inhibit the catalysis by modifying the RT enzyme.
The result of this study has been published in BioMed Central and the research was carried out by two researchers, Vasudevan Achuthan and Jeffrey J DeStefano from the Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, USA. In this study, researchers used PCR-based and plasmid-based alpha complementation assay, as well as steady-state misinsertion (faulty insertion of nucleotides) and misincorporation (faulty incorporation of nucleotides), assay during the reverse transcription process to examine the fidelity of the reverse transcriptase enzyme with different divalent cations like Mn2+, Co2+, and Zn2+.
Results revealed that the fidelity of the DNA synthesis catalyzed by the HIV-1 reverse transcriptase enzyme was around 2.5 times greater in Zn2+ as compared to Mg2+ ion at an optimized condition for nucleotides catalyzed. With this condition, reverse transcriptase extended the primer with mismatched 3’-nucleotide and inserted incorrect nucleotides less efficiently using the Zn2+ ions than Mg2+ ions. That means in the presence of the Zn2+ ion, the reverse transcription is much accurate but proceeds very slowly. According to the previous studies, they observed that Mn2+ and Co2+ cause decreased.
That means in the presence of the Zn2+ ion, the reverse transcription is much accurate but proceeds very slowly. According to the previous studies, they observed that Mn2+ and Co2+ cause decreased the fidelity of reverse transcriptase catalysis at a higher concentration around 6mM. However, at a lower concentration, the effect of Mn2+ and Co2+ on the RT enzyme remained similar to that of Mg2+ that is optimal for catalysis.
In conclusion, DNS synthesis by HIV RT in the presence of Zn2+ is highly accurate even more accurate than in the case of Mg2+ ions but proceeds very slowly. While, other divalent cations like Mn2+ and Co2+ showed fidelity levels comparable with Mg2+ at optimal conditions (at a lower concentration), but with less accuracy.
However, at a higher concentration, they (Mn2+ and Co2+) are all mutagenic in nature, which means their accuracy decreases with an increase in concentration. All these indicate that catalysis of RT with these divalent cations is not intrinsically mutagenic (because they are present in a very low concentration in the cellular environment, not sufficient to show mutagenesis), but the mutagenicity in previous reports may be due to some other mechanisms that need further investigation.
Reference: BioMed Central