T4 polynucleotide kinase (T4 PNK) and T4 DNA ligase are two important repair enzymes that play a significant role in maintaining the stability and integrity of genome. Here, we proposed a multiple primers-mediated exponential rolling circle amplification strategy for label-free and highly sensitive fluorescent analysis of T4 PNK and T4 DNA ligase activity. Firstly, we designed a target strand that contained two C-rich sequences, a complementary sequence of the primer, and three cleavage sites of Nt.BbvCI scattered among the three sequences. The 5′-hydroxyl terminus of target strand was catalyzed by T4 PNK to form a phosphorylated target strand. After the phosphorylated target strand was combined with the primer, T4 DNA ligase catalyzed the formation of circular DNA. Then, the primer triggered an exponential rolling circle amplification reaction along the circular DNA template, exponentially generating G-rich sequences. N-methyl mesoporphyrin IX as signal molecules specifically bound to the G-quadruplexs folded by G-rich sequences, generating a detectable fluorescent signal. Benefiting from exponential signal growth, this strategy showed extremely high detection sensitivity with detection limits of 8.11 × 10 −5 U mL −1 of T4 PNK and 3.07 × 10 −4 U mL −1 of T4 DNA ligase, respectively. In addition, the proposed strategy exhibited excellent inhibitor evaluation effects for two repair enzymes, and could detect T4 PNK in HeLa cell lysate. The obtained results showed that the proposed strategy had excellent application prospects in disease diagnosis and treatment evaluation.
Flap endonuclease I (FEN1) is a structure-specific nuclease that participates in DNA repair, and its overexpression is related to an increased risk of cancer. Currently, few FEN1 assays can meet the requirements for diagnostic purposes due to their high complexity, low specificity, and limited sensitivity. Herein, we developed a biosensor adopting synthetic biology strategy, called CLAIM (cleavage-ligation-activation-involved monitoring) for FEN1 quantification. CLAIMintegrates ligation-based T7 promoter repair, RNA generation, and CRISPR/Cas13a. FEN1 cleavages the DNA probe with a 5′-flap to generate a nick site that can be ligated to form a T7 promoter. Subsequent transcription produces abundant RNA that can activate Cas13a, generating a fluorescence signal due to the trans -cleavage of Cas13a to a fluorogenic reporter. CLAIM was able to detect FEN1 with low femtomolar sensitivity, and its accuracy was validated using samples of cancer and non-tumorigenic cell lines. Interestingly, we found that the utilization of thermostable T4 DNA ligase is critical to make the cascade of FEN1 cleavage, ligation, and transcription take place in one-pot. CLAIM was also repurposed for validating FEN1 inhibitors, indicating its potential in drug screening. This work provides a diagnostic tool for FEN1 analysis and opens up opportunities for FEN1 biosensing and related drug discovery.
Lu Lu,Jing Cao Si,Zhong Feng Gao,Yu Zhang,Jing Lei Lei,Hong Qun Luo,Nian Bing Li
A dual strategy that combines the adenosine triphosphate (ATP)-dependent enzymatic ligation reaction with self-cleaving DNAzyme-amplified electrochemical detection is employed to construct the biosensor. In this design, the methylene blue-labeled hairpin-structured DNA was self-assembled onto a gold electrode surface to prepare the modified electrode through the interaction of Au–S bond. In the procedure of ATP-dependent ligation reaction, when the specific cofactor ATP was added, the two split oligonucleotide fragments of 8-17 DNAzyme were linked by T4 DNA ligase and then released to hybridize with the labeled hairpin-structured DNA substrate. The linked 8-17 DNAzyme catalyzes the cleavage of the hairpin-structured substrate by the addition of Zn 2+ , causing the methylene blue which contains high electrochemical activity to leave the surface of the gold electrode, therefore generating a dramatic decrease of electrochemical signal. The decrease of peak current was readily measured by square wave voltammetry and a relatively low detection limit (0.05 nM) was obtained with a linear response range from 0.1 to 1000 nM. By taking advantage of the highly specific cofactor dependence of the DNA ligation reaction, the proposed ligation-induced DNAzyme cascades demonstrate ultrahigh selectivity toward the target cofactor ATP. A catalytic and molecular beacons strategy is further adopted to amplify the electrochemical signal detection achieved by cycling and regenerating the 8-17 DNAzyme to realize enzymatic multiple turnover, thus one DNAzyme can catalyze the cleavage of several hairpin-structured substrates, which improves the sensitivity of the newly designed electrochemical sensing system.
危险品化学品经营许可证（带存储）