G-Quadruplexes Formation by the IC9orf72/I Nucleotide Repeat Expansion d[sub.n] and Conformation Regulation by Fangchinoline

• Published in: Molecules (Basel, Switzerland) Vol. 28; no. 12
• Main Authors: Zhang, Yun, Huang, Junliu, Yu, Kainan, Cui, Xiaojie
• Format: Journal Article
• Language: English
• Published: MDPI AG 01.06.2023
• Subjects: Health aspects; RNA; China
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28124671

The G-quadruplex (GQ)-forming hexanucleotide repeat expansion (HRE) in the C9orf72 (C9) gene has been found to be the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (collectively, C9ALS/FTD), implying the great significance of modulating C9-HRE GQ structures in C9ALS/FTD therapeutic treatment strategies. In this study, we investigated the GQ structures formed by varied lengths of C9-HRE DNA sequences d(GGGGCC)[sub.4] (C9-24mer) and d(GGGGCC)[sub.8] (C9-48mer), and found that the C9-24mer forms anti-parallel GQ (AP-GQ) in the presence of potassium ions, while the long C9-48mer bearing eight guanine tracts forms unstacked tandem GQ consisting of two C9-24mer unimolecular AP-GQs. Moreover, the natural small molecule Fangchinoline was screened out in order to be able to stabilize and alter the C9-HRE DNA to parallel GQ topology. Further study of the interaction of Fangchinoline with the C9-HRE RNA GQ unit r(GGGGCC)[sub.4] (C9-RNA) revealed that it can also recognize and improve the thermal stability of C9-HRE RNA GQ. Finally, use of AutoDock simulation results indicated that Fangchinoline binds to the groove regions of the parallel C9-HRE GQs. These findings pave the way for further studies of GQ structures formed by pathologically related long C9-HRE sequences, and also provide a natural small-molecule ligand that modulates the structure and stability of C9-HRE GQ, both in DNA and RNA levels. Altogether, this work may contribute to therapeutic approaches of C9ALS/FTD which take the upstream C9-HRE DNA region, as well as the toxic C9-HRE RNA, as targets.