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Measurement of intercolumnar forces between parallel guanosine four-stranded helices
1Istituto di Scienze Fisiche, Facoltà di Medicina e Chirurgia, Università di Ancona, Italy. mariani@anvax1.cineca.it
Biophysical Journal
|June 1, 1996
Summary
Deoxyguanosine-5'-monophosphate forms stable helical structures in solution. Hydration repulsion, not electrostatic forces, dominates interactions between these helices at close range.
Area of Science:
- Biophysics
- Supramolecular Chemistry
- Materials Science
Background:
- Deoxyguanosine-5 -monophosphate (dGMP) self-associates in aqueous solutions.
- These associations form stable hexagonal and cholesteric columnar phases.
- The structural unit is a four-stranded helix of Hoogsteen-bonded guanosine quartets.
Purpose of the Study:
- To investigate the forces governing the interactions between deoxyguanosine helices.
- To elucidate the nature and contributions of electrostatic and short-range forces.
- To understand the role of ionic conditions on these forces.
Main Methods:
- Osmotic stress method was employed to measure force per unit length versus interaxial distance.
- Experiments were conducted under various ionic conditions.
- Analysis focused on distinguishing electrostatic and short-range repulsive forces.
Main Results:
- Two distinct force contributions were identified: electrostatic and short-range repulsion.
- Electrostatic forces are long-range and salt-dependent.
- Short-range repulsion (<30-32 Å) is exponential, salt-insensitive, and prevents helix coalescence, characteristic of hydration forces.
Conclusions:
- The dominant force between deoxyguanosine helices at close contact is hydration repulsion.
- The observed decay length (0.7 Å) arises from coupled water solvent and helical hydrophilic group structures.
- Results align with hydration force studies on other macromolecules and confirm structure-force correlations.