Head-to-head bis-hairpin polyamide minor groove binders and their conjugates with triplex-forming oligonucleotides: studies of interaction with target double-stranded DNA

J Biomol Struct Dyn. 2007 Aug;25(1):61-76. doi: 10.1080/07391102.2007.10507156.

Abstract

Two hairpin hexa(N-methylpyrrole)carboxamide DNA minor groove binders (MGB) were linked together via their N-termini in head-to-head orientation. Complex formation between these bis-MGB conjugates and target DNA has been studied using DNase I footprinting, circular dichroism, thermal dissociation, and molecular modeling. DNase I footprint revealed binding of these conjugates to all the sites of 492 b.p. DNA fragment containing (A/T)(n)X(m)(A/T)(p) sequences, where n>3, p>3; m=1,2; X = A,T,G, or C. Binding affinity depended on the sequence context of the target. CD experiments and molecular modeling showed that oligo(N-methylpyrrole)carboxamide moieties in the complex form two short antiparallel hairpins rather than a long parallel head-to-head hairpin. Binding of bis-MGB also stabilized a target duplex thermodynamically. Sequence specificity of bis-MGB/DNA binding was validated using bis-conjugates of sequence-specific hairpin (N-methylpyrrole)/(N-methylimidazole) carboxamides. In order to increase the size of recognition sequence, the conjugates of bis-MGB with triplex-forming oligonucleotides (TFO) were synthesized and compared to TFO conjugated with single MGB hairpin unit. Bis-MGB-oligonucleotide conjugates also bind to two blocks of three and more A.T/T.A pairs similarly to bis-MGB alone, independently of the oligonucleotide moiety, but with lower affinity. However, the role of TFO in DNA recognition was demonstrated for mono-MGB-TFO conjugate where the binding was detected mainly in the area of the target sequence consisting of both MGB and TFO recognition sites. Basing on the molecular modeling, three-dimensional models of both target DNA/bis-MGB and target DNA/TFO-bis-MGB complexes were built, where bis-MGB forms two antiparallel hairpins. According to the second model, one MGB hairpin is in the minor groove of 5'-adjacent A/T sequence next to the triplex-forming region, whereas the other one occupies the minor groove of the TFO binding polypurine tract. All these data together give a key information for the construction of MGB-MGB and MGB-oligonucleotide conjugates possessing high specificity and affinity for the target double-stranded DNA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amides / chemistry
  • Base Sequence
  • Circular Dichroism
  • DNA* / chemistry
  • DNA* / metabolism
  • Deoxyribonuclease I / metabolism
  • Macromolecular Substances
  • Models, Molecular
  • Molecular Sequence Data
  • Molecular Structure
  • Nucleic Acid Conformation*
  • Oligonucleotides / chemistry*
  • Oligonucleotides / genetics
  • Oligonucleotides / metabolism*
  • Organophosphates / chemistry

Substances

  • Amides
  • Macromolecular Substances
  • Oligonucleotides
  • Organophosphates
  • mono-n-butylphosphoric acid
  • DNA
  • Deoxyribonuclease I