Guanine quadruplexes (GQ) are four-stranded DNA structures formed by guanine-rich DNA sequences. Formation of GQs inhibits cancer cell survival, but detecting GQs in vivo has proved difficult, in part because of GQ structural diversity. Development of GQ-selective fluorescent reporters that are sensitive to GQ structure would enhance our ability to quantify the number and location of GQs, ultimately advancing biological studies of quadruplex relevance and functions. N-methyl mesoporphyrin IX (NMM) interacts selectively with parallel-stranded GQs. In addition, its fluorescence is sensitive to the presence of DNA, making this ligand a possible candidate for a quadruplex probe. We have investigated the effect of DNA secondary structure and GQ strand orientation on NMM fluorescence. Consistent with NMMs strong preference for parallel-stranded GQs, we find that NMM fluorescence increases significantly by about 60-fold in the presence of these structures (IL1, G4, G8, VEGF, cMyc, and cKit2). Increases of about 40-fold are observed when NMM is presented with hybrid quadruplexes (cKit1, G4TERT, Bcl-2, Tel22, and 26TelG4). Antiparallel GQs (Tel22, TBA, 26TelG4, and G4T4G4, all in sodium buffer) cause only small increase in NMM fluorescence, about 9-fold. Non-quadruplex DNA structures such as single-stranded DNA, duplex, or i-motif induce no change in NMM fluorescence. We conclude that NMM could be a promising fluorescent probe for detecting quadruplex structures and for differentiating them on the basis of their strand orientation.
Citation: FEBS Journal
Pub Type: Journals
guanine quadruplex, N-methylmesoporphyrin IX, fluorescence spectroscopy, telomeric DNA, guanine quartet