P. Mariani et al., HELIX-SPECIFIC INTERACTIONS INDUCE CONDENSATION OF GUANOSINE 4-STRANDED HELICES IN CONCENTRATED SALT-SOLUTIONS, Biophysical journal, 74(1), 1998, pp. 430-435
Deoxyguanosine-5'-monophosphate in water self-associates into stable s
tructures, which include liquid-crystalline hexagonal and cholesteric
phases. The structural unit is a four-stranded helix, composed of stac
ked Hoogsteen-bonded guanosine quartets. By using the osmotic stress m
ethod, we recently measured the force between helices in KCI solutions
up to 2 M. In addition to the long-range electrostatic force, a short
-range hydration repulsive contribution was recognized. The hydration
repulsion is exponential, and shows a decay length independent from th
e ionic strength of the solution. Here, we report that more concentrat
ed KCI solutions cause condensation of the guanosine helix in a hexago
nal phase with constant equilibrium separation of similar to 7 Angstro
m between helix surfaces. Long-range attraction, which induces the sel
f-assembly, and short-range repulsion, which prevents the contact betw
een the helices, are implied. By using osmotic stress, the force neede
d to push helices closer from the spontaneously assumed position has b
een measured. The attractive force was then estimated as a difference
between the net force and the repulsive contribution, revealing an exp
onential decay length about two times larger than that of the short-ra
nge repulsion. The agreement with the helix interaction theory introdu
ced recently by Kornyshev and Leikin (Kornyshev, A. A., and S. Leikin,
1997, Theory of interaction between helical molecules. J. Phys. Chem.
107:3656-3674) suggests that the repulsive and attractive forces orig
inate from helix-specific interactions.