Positional Impact of Fluorescently Modified G‑Tetrads within Polymorphic Human Telomeric G‑Quadruplex Structures

Emissive C8-aryl-2′-deoxyguanosines placed within G-tetrads of G-quadruplex structures are useful probes for distinguishing G-quadruplexes from duplex structures using fluorescence spectroscopy. Here, we report the positional impact of C8-furyl-dG (^FurdG) on G-quadruplex folding in the human telomere 22-mer oligonucleotide (HTelo22, (d­[AG₃(T₂AG₃)₃])). The ^FurdG probe was inserted into four different positions within the three unique G-tetrads of HTelo22, and G-quadruplex folding was monitored by UV–vis thermal denaturation, circular dichroism, and fluorescence spectroscopy. Our studies demonstrate the impacts of C8-aryl-dG adduct formation on G-quadruplex polymorphism in K⁺ solution and in the presence of the additives and cosolutes, CH₃CN, polyethylene glycol (PEG-600), and N-methyl mesoporphyrin IX (NMM). Our experiments predict that C8-aryl-dG derivatives can serve as useful tools for various in vitro studies aimed at understanding both the implications of DNA adduct formation within G-quadruplex structures and the unique implications imposed by various folding topologies on biological function/recognition.