Abstract
The G-quadruplex, a four-stranded DNA structure with stacked guanine tetrads (G-quartets), has recently been attracting attention because of its critical roles in vitro and in vivo. In particular, the G-quadruplex functions as ligands for metal ions and aptamers for various molecules. Interestingly, the G-quadruplex can show peroxidase-like activity with an anionic porphyrin, iron (III) protoporphyrin IX (hemin). Importantly, hemin binds to G-quadruplexes with high selectivity over single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), which is attributable to an electrostatic repulsion of phosphate groups in ssDNA and dsDNA. The G-quadruplex and hemin-G-quadruplex complex allow development of sensing techniques to detect DNA, metal ions and proteins. In addition to hemin, anionic phthalocyanines also bind to the G-quadruplex formed by human telomere DNA, specifically over ssDNA and dsDNA. Since the binding of anionic phthalocyanines to the G-quadruplex causes an inhibition of telomerase activity, which plays a role in the immortal growth of cancer cells, anionic phthalocyanines are promising as novel anticancer drug candidates. This review focuses on the specific binding of hemin and anionic phthalocyanines to G-quadruplexes and the applications in vitro and in vivo of this binding property.
Highlights
The fabrication of functional nanomaterials, which includes functional dyes [1,2,3], carbon nanomaterials [4,5,6] and nanoparticles [6,7,8,9], by biomolecules such as nucleic acids, proteins and lipids has recently been opening up an entire new and exciting research area
The key point is the specific binding of hemin to the G-quadruplex because the system can not work if hemin binds to single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) nonspecifically and the complexes exert peroxidase-like activity
The cationic ligands nonspecifically bind to ssDNA and dsDNA electrostatically [20,22,23,25]
Summary
The fabrication of functional nanomaterials, which includes functional dyes (porphyrins and phthalocyanines) [1,2,3], carbon nanomaterials (fullerenes, carbon nanotubes, or graphenes) [4,5,6] and nanoparticles (gold nanoparticles, magnetic nanoparticles, or quantum dots) [6,7,8,9], by biomolecules such as nucleic acids, proteins and lipids has recently been opening up an entire new and exciting research area. G-rich sequences can fold to form various types of G-quadruplex conformations depending on the sequences and the experimental conditions (e.g., coexisting metal ion, metal ion concentration and degree of molecular crowding) (Figure 1B) [11,12,13,14] These findings combined with the peroxidase-like activity of the hemin-G-quadruplex complex have stimulated development of various applications, mainly detection techniques targeting DNA, proteins and metal ions [15,16,17,18]. The specificity of hemin binding to G-quadruplexes is significantly high This specific binding is attributable to an electrostatic repulsion between the carboxyl groups of hemin and the phosphate groups of DNA, leading to inhibition of hemin binding to ssDNA and dsDNA. We will briefly describe the implications of some other interesting applications
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