ddGTP

ddGTP (2’, 3’-Dideoxyguanosine 5’-triphosphate) is a dideoxynucleotide used as a chain terminator in DNA sequencing^[1]. Unlike dGTP, ddGTP lacks hydroxyl groups at both the 2’ and 3’ positions of the ribose moiety. This structural feature prevents the formation of a 3’, 5’-phosphodiester bond after being incorporated by polymerase into a growing DNA strand, resulting in termination of DNA synthesis^[2]. ddGTP is commonly employed in cycle sequencing, enzymatic mechanism studies, and the generation of RNA or DNA sequences that cannot be extended by polymerases or ligated by DNA ligases^[3].

In vitro, ddGTP (＜1μM) strongly inhibits DNA polymerase α activity in the presence of Mn²⁺ by competing with the natural substrate dGTP for the enzyme’s binding site, exhibiting an inhibition constant (K_i) of 0.035μM^[4]. ddGTP effectively inhibits the reverse transcriptase of human and simian immunodeficiency viruses (HIV and SIV), with K_i values of 0.009μM and 0.011μM, respectively^[5]. Following incubation with TS30- and TS60-modified biosensors and Jurkat T cells for 3h in the presence of 0.2mM ddGTP, a subsequent 1h incubation in 10μM thiazole orange (TO) solution was performed. The mean fluorescence intensity (MFI) of the ddGTP-treated sensors (MFI=157) was significantly lower than that of the positive control group (MFI=261)^[6]. Starch-TEPA/ddGTP complex (containing 1mg/mL starch-TEPA and 0.3mg/mL ddGTP) incubated with A549 cells at 37℃ for 4h exhibited high biological activity (99%), significantly surpassing the cell-killing effect of free ddGTP^[7].

References:
[1] SANGER F, NICKLEN S, COULSON A R. DNA sequencing with chain-terminating inhibitors[J]. Proceedings of the National Academy of Sciences, 1977, 74(12): 5463-5467.
[2] ALPHEY L. Chain Termination (Sanger Dideoxy) Method[M]// DNA Sequencing. New York: Garland Science, 2023: 15-25.
[3] EREN K, TAKTAKOĞLU N, PIRIM I. DNA sequencing methods: from past to present[J]. The Eurasian Journal of Medicine, 2022, 54(Suppl 1): S47.
[4] ONO K, NAKANE H. Utilization of 2', 3'-dideoxyguanosine 5'-triptiosphate as an inhibitor and substrate for DNA polymerase α[J]. Biomedicine & Pharmacotherapy, 1990, 44(2): 115-121.
[5] WU J C, CHERNOW M, BOEHME R E, et al. Kinetics and inhibition of reverse transcriptase from human and simian immunodeficiency viruses[J]. Antimicrobial Agents and Chemotherapy, 1988, 32(12): 1887-1890.
[6] DÍAZ-CARTAGENA D C, HERNÁNDEZ-CANCEL G, BRACHO-RINCÓN D P, et al. Label-free telomerase activity detection via electrochemical impedance spectroscopy[J]. ACS Omega, 2019, 4(16): 16724-16732.
[7] KANBER E, YAMADA H, LORETZ B, et al. Design of polyamine-grafted starches for nucleotide analogue delivery: in vitro evaluation of the anticancer activity[J]. Bioconjugate Chemistry, 2016, 27(10): 2431-2440.

ddGTP（2’, 3’-Dideoxyguanosine 5’-triphosphate）是一种在DNA测序中被用作链终止剂的双脱氧核苷酸^[1]。与dGTP不同，ddGTP在核糖的2’和3’位置均缺少羟基，使得在被聚合酶掺入新生DNA链后无法形成3’,5’-磷酸二酯键，从而导致DNA合成反应被迫终止^[2]。ddGTP常用于循环测序、酶机制研究以及生成无法通过聚合酶延伸或通过DNA连接酶连接的RNA和DNA序列^[3]。

在体外，ddGTP（＜1μM）在Mn²⁺存在条件下，可通过与天然底物dGTP竞争酶的结合位点实现强效抑制DNA聚合酶α的活性，抑制常数K_i为0.035μM^[4]。ddGTP可以有效抑制人和猴免疫缺陷病毒（HIV和SIV）逆转录酶的活性，对HIV和SIV逆转录酶的Ki分别为0.009μM和0.011μM^[5]。ddGTP（0.2mM）与经TS30和TS60修饰的生物传感器及Jurkat T细胞共孵育3h，后在10μM thiazole orange（TO）溶液中继续孵育1h，与ddGTP共孵育的传感器平均荧光强度（MFI=157）远低于阳性对照组（MFI=261）^[6]。Starch-TEPA/ddGTP复合物（starch-TEPA浓度1mg/mL；ddGTP浓度0.3mg/mL）与A549细胞在37℃下共孵育4h，展现出极高的生物活性（99%），显著优于游离ddGTP对细胞的杀伤作用^[7]。