Synchrotron Radiation Circular Dichroism of Various G-Guadruplex Structures

• Here we report synchrotron radiation circular dichroism spectra of various G-quadruplexes from 179 to 350 nm, and a number of bands in the vacuum ultraviolet (VUV) are reported for the first time. For a tetramolecular parallel structure, the strongest band in the spectrum is a negative band in the VUV at 182 nm; for a bimolecular antiparallel structure with diagonal loops, a new strong positive band is found at 190 nm; for a bimolecular parallel structure with edgewise loops, a strong positive band at 189 nm is observed; and for a self-folded chair-type structure, the strongest band in the spectrum is a positive band at 187 nm. For the tetramolecular parallel structure, the CD signals at all wavelengths are dominated by contributions from quartets of G bases, and the signal strength is approximately proportional to the number of quartets. Our experiments on well-characterized G-quadruplex structures lead us to question past attributions of CD signals to helix handedness and G quartet polarity. Although differences can be observed in the VUV region for the various quadruplex types, there do not appear to be clear-cut spectral features that can be used to identify specific topological features. It is suggested that this is because a dominant positive band in the VUV seen near 190 nm in all quadruplex structures is due to intrastrand guanine guanine base stacking. However, our spectra can serve as reference spectra for the G-quadruplex structures investigated and, not least, to benchmark theoretical calculations and empirical models.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

synchrotron radiation circular dichroism

guanine quadruplexes

quartet polarity

Physics

Fysik

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