Effect Of Er³⁺, Gd³⁺ And La³⁺ On The Taq DNA Polymerase Activity

With the wide use of rare earths in agriculture, industry, livestock agriculture and modern medicine areas, they inevitably enter the environment, furthermore to organisms through eco-system and the food chain. Therefore, the action mechanism of rare earth on the organisms has attracted most scientific interest. Many research results showed that rare earths could indeed damage the organism DNA, but a few studies were performed about the damage mechanism, especially in level of DNA molecules.This study investigated DNA damage mechanism induced by rare-earth ions, which was started mainly from the role of rare earth on TaqDNA polymerase. By adding different concentrations of rare earth ions (La³⁺,Gd³⁺ and Er³⁺) in the PCR reaction system, the effects of rare earth on Taq DNA polymerase were measured through PCR products concentration and base changes in the DNA sequence. Then ultraviolet spectroscopy and circular dichroism method were used to analyze the changes of TaqDNA polymerase conformation.The experimental results showed that the three types of rare earth ions were added respectively in the PCR reaction. When low concentrations of La³⁺and Gd³⁺, between 1.0×10^-3mol/L and 1.0×10^-8mol/L, were adopted, it could promote the PCR reaction, while high concentration could inhibit the reaction. The higher the concentration were, the stronger inhibition were. When the concentration was higher than 1.0×10^-2mol/L, DNA replication was inhibited completely. However, Er³⁺ has strong inhibition effect in general, even when its concentration was lower. There was no activation; PCR products sequence revealed that many bases were mismatched; La³⁺, Er³⁺ and Gd³⁺ could make UV-visible absorption spectrum of Taq DNA polymerase change, and the higher the rare earth ion concentration was, the lower the absorption peak of Taq DNA polymerase at 222nm was; Circular dichroism rerults showed that rare earth ions could affect the secondary structure of TaqDNA polymerase, and the low concentrations rare earth ions could causeα-helix content of TaqDNA polymerase to increase and the high concentration could cause it to decrease.Experimental results showed that rare earth ions could affect the three-dimensional conformation of TaqDNA polymerase, which not only changed replication activity of the enzyme but also could cause base mismatch during DNA replication. Based on these results, it concludes that the rare earth can lead to mutagen. One of the mechanisms causing gene mutation might be to change of the Taq DNA polymerase conformation. It interfers with the enzyme-substrate-dNTP binding site and further causes replication mismatch.