Structural and electrostatic effects on binding of trivalent cations to double-stranded and single-stranded poly[d...

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Cation binding significantly influences DNA structure and stability.
• Understanding polycation-DNA interactions is crucial for various biological processes.

Purpose of the Study:

• To investigate the binding of three trivalent cations (spermidine, me8spermidine, hexammine cobalt(III)) to poly[d(AT)].poly[d(TA)].
• To determine the thermodynamic parameters of cation binding to both double-stranded and single-stranded DNA.
• To compare the binding affinities and structural effects of these cations on DNA.

Main Methods:

• Thermal melting profile analysis of poly[d(AT)].poly[d(TA)] in the presence of varying concentrations of trivalent cations.
• Application of McGhee's (1976) theory for ligand-DNA interactions.
• Estimation of association constants (Kh, Kc) and binding site sizes (nh, nc).

Main Results:

• Binding parameters for spermidine and hexammine cobalt(III) to double-helical DNA align with equilibrium dialysis and counterion condensation theory.
• The three cations exhibit distinct binding affinities for single-stranded DNA, despite their identical charges.
• Structural analysis suggests poly[d(AT)] becomes less elongated with spermidine and hexammine cobalt(III) compared to me8spermidine.

Conclusions:

• Trivalent cations display differential binding behavior towards single-stranded DNA.
• The specific chemical structure of the cation, beyond its charge, influences its interaction with single-stranded DNA.
• These findings contribute to understanding the complex interplay between polycations and nucleic acid conformation.