Molecular modeling and biophysical analysis of the c-MYC NHE-III1 silencer element

J Mol Model. 2008 Feb;14(2):93-101. doi: 10.1007/s00894-007-0254-z. Epub 2007 Dec 18.

Abstract

G-Quadruplex and i-Motif-forming sequences in the promoter regions of several oncogenes show promise as targets for the regulation of oncogenes. In this study, molecular models were created for the c-MYC NHE-III(1) (nuclease hypersensitivity element III(1)) from two 39-base complementary sequences. The NHE modeled here consists of single folded conformers of the polypurine intramolecular G-Quadruplex and the polypyrimidine intramolecular i-Motif structures, flanked by short duplex DNA sequences. The G-Quadruplex was based on published NMR structural data for the c-MYC 1:2:1 loop isomer. The i-Motif structure is theoretical (with five cytosine-cytosine pairs), where the central intercalated cytosine core interactions are based on NMR structural data obtained for a tetramolecular [d(A(2)C(4))(4)] model i-Motif. The loop structures are in silico predictions of the c-MYC i-motif loops. The porphyrin meso-tetra(N-methyl-4-pyridyl)porphine (TMPyP4), as well as the ortho and meta analogs TMPyP2 and TMPyP3, were docked to six different locations in the complete c-MYC NHE. Comparisons are made for drug binding to the NHE and the isolated G-Quadruplex and i-Motif structures. NHE models both with and without bound cationic porphyrin were simulated for 100 ps using molecular dynamics techniques, and the non-bonded interaction energies between the DNA and porphyrins calculated for all of the docking interactions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biophysics*
  • DNA / chemistry
  • Down-Regulation / physiology
  • G-Quadruplexes
  • Humans
  • Models, Molecular*
  • Nucleic Acid Conformation*
  • Proto-Oncogene Proteins c-myc / genetics*
  • Silencer Elements, Transcriptional / genetics*

Substances

  • MYC protein, human
  • Proto-Oncogene Proteins c-myc
  • DNA