Biophysical studies of the c-MYC NHE III1 promoter

Model quadruplex interactions with a cationic porphyrin

Matthew W. Freyer, Robert Buscaglia, Kimberly Kaplan, Derek Cashman, Laurence Hurley, Edwin A. Lewis

Research output: Contribution to journalArticle

107 Citations (Scopus)

Abstract

Regulation of the structural equilibrium of G-quadruplex-forming sequences located in the promoter regions of oncogenes by the binding of small molecules has shown potential as a new avenue for cancer chemotherapy. In this study, microcalorimetry (isothermal titration calorimetry and differential scanning calorimetry), electronic spectroscopy (ultraviolet-visible and circular dichroism), and molecular modeling were used to probe the complex interactions between a cationic porphryin mesotetra (N-methyl-4-pyridyl) porphine (TMPyP4) and the c-MYC PU 27-mer quadruplex. The stoichiometry at saturation is 4:1 mol of TMPyP4/c-MYC PU 27-mer G-quadruplex as determined by isothermal titration calorimetry, circular dichroism, and ultraviolet-visible spectroscopy. The four independent TMPyP4 binding sites fall into one of two modes. The two binding modes are different with respect to affinity, enthalpy change, and entropy change for formation of the 1:1 and 2:1, or 3:1 and 4:1 complexes. Binding of TMPyP4, at or near physiologic ionic strength ([K+] = 0.13 M), is described by a "two-independent-sites model." The two highest-affinity sites exhibit a K1 of 1.6 x 107 M-1 and the two lowest-affinity sites exhibit a K2 of 4.2 x 105 M -1. Dissection of the free-energy change into the enthalpy- and entropy-change contributions for the two modes is consistent with both "intercalative" and "exterior" binding mechanisms. An additional complexity is that there may be as many as six possible conformational quadruplex isomers based on the sequence. Differential scanning calorimetry experiments demonstrated two distinct melting events (Tm1 = 74.7°C and Tm2 = 91.2°C) resulting from a mixture of at least two conformers for the c-MYC PU 27-mer in solution.

Original languageEnglish (US)
Pages (from-to)2007-2015
Number of pages9
JournalBiophysical Journal
Volume92
Issue number6
DOIs
StatePublished - Mar 2007

Fingerprint

Porphyrins
G-Quadruplexes
Calorimetry
Differential Scanning Calorimetry
Entropy
Circular Dichroism
Spectrum Analysis
Oncogenes
Genetic Promoter Regions
Osmolar Concentration
Freezing
Dissection
Binding Sites
Drug Therapy
tetra(4-N-methylpyridyl)porphine
Neoplasms

ASJC Scopus subject areas

  • Biophysics

Cite this

Biophysical studies of the c-MYC NHE III1 promoter : Model quadruplex interactions with a cationic porphyrin. / Freyer, Matthew W.; Buscaglia, Robert; Kaplan, Kimberly; Cashman, Derek; Hurley, Laurence; Lewis, Edwin A.

In: Biophysical Journal, Vol. 92, No. 6, 03.2007, p. 2007-2015.

Research output: Contribution to journalArticle

Freyer, Matthew W. ; Buscaglia, Robert ; Kaplan, Kimberly ; Cashman, Derek ; Hurley, Laurence ; Lewis, Edwin A. / Biophysical studies of the c-MYC NHE III1 promoter : Model quadruplex interactions with a cationic porphyrin. In: Biophysical Journal. 2007 ; Vol. 92, No. 6. pp. 2007-2015.
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