Mercury-induced DNA polymorphism: probing the conformation of mercury(II)-DNA via staphylococcal nuclease digestion and circular dichroism measurements

Abstract

Exposing native calf thymus DNA to increasing concentrations of Hg(ClO4)2 not only produces dramatic changes in its circular dichroism (CD) but results also in the decrease, and ultimate cessation, of endonucleolytic DNA cleavage by staphylococcal nuclease. Let r = [moles of added Hg(II)]/[mole of DNA base]: the conservative CD spectrum of the DNA B-form becomes nonconservative in appearance at 0.01 less than r less than 0.12 (resembling DNA in C-form geometry) and assumes the spectral characteristics of a left-handed DNA double helix at 0.12 less than r less than or equal to 1.0. DNA cleavage proceeds at or near the rates exhibited by untreated DNA at 0 less than r less than 0.08. At Hg(II) levels of 0.08 less than r less than 0.5, the rate of DNA hydrolysis decreases monotonically with increasing Hg(II) concentrations, and at r greater than 0.4, DNA cleavage ceases. Both the CD changes and the changes in the rate of DNA digestion are totally reversible upon the removal of Hg(II), at least up to r = 1.0, demonstrating that Hg(II) keeps all base pairs in register. For comparison purposes, native calf thymus DNA was also treated with methylmercury [CH3Hg(II)], an agent known to disrupt the secondary structure of DNA. The treatment yielded single-stranded methylmercurated DNA with preserved right-handed helix screwness. In addition, this DNA is digested by staphylococcal nuclease much more rapidly than double-stranded control DNA. Lastly, neither the CD nor the cleavage rate changes are reversible upon the removal of methylmercury.(ABSTRACT TRUNCATED AT 250 WORDS)

A DNA-based assay for toxic chemicals in wastewater

“…Mercury is one of the most toxic metal ions [26]. It affects the conformation or structure, or both, of DNA depending on its concentration.…”

“…It affects the conformation or structure, or both, of DNA depending on its concentration. Mercury binds preferentially to DNA bases with the relative affinities T > G >> A, C [26], significantly reducing DNA viscosity [17], which can be explained by induced changes in the DNA helix [15]. This leads to a fourfold increase in the NMR signal, presumably because of the spin-spin T 2 relaxation being inversely related to the solution viscosity [27].…”

Differential Effect of Hg(II) on [d(A)n · d(T)n] and [d(A-T)n · d(A-T)n] Sequences: Circular Dichroism (CD) Measurements and Endonuclease Digestion Studies Using Poly[d(A) · d(T)] and Poly[d(A-T) · d(A-T)] as Substrates

“…, It was fu rth er found th a t the reversible inversion o f the long-w ave length C o tto n b an d o f m ercurated calf thym us D N A (m axim um at 273 nm ) from positive to neg ative chirality is accom panied by an equally revers ible decrease in the rate o f digestion o f the D N A by staphylococcal nuclease [3], The enzym e is know n n o t to digest left-handed D N A [5].…”

“…In form ation regarding the com m ercial suppliers as well as analytical properties o f the other chem icals used in this w ork can be found elsewhere [1][2][3][4], C ircular dichroism m easurem ents were p e r form ed at 25 °C as described [1][2][3][4], The polym ers, dissolved in 0.1 m N aC 1 0 4, 5 mM cacodylic acid buffer, pH 6.9, were at a final concentration near 0.84 ,4260-units (about 42 (ig/ml). Polym er concen tratio n s were evaluated by using the m olar absorptivities o f 6000 and 6650 (l/m ol(P)/cm ) at 260 nm The m ethodology o f the enzym atic digestion ex perim ents has been described in detail elsewhere [3], D N ase I hydrolysis rates were determ ined in 0.1 m N aC 1 0 4, 5 mM cacodylic acid buffer, pH 6.9 (37 °C); staphylococcal nuclease rates were m eas ured in 0.1 m N aC 104, 5 mM boric acid buffer, p H 8.9 (37 °C). Finally, all C D changes are com pletely reversi ble u p o n the rem oval o f H g(II) from the polym ers.…”

Hg²⁺-Trapping Beads: Hg²⁺-Specific Recognition through Thymine–Hg(II)–Thymine Base Pairing

“…[22][23][24][25] New insights were recently reported by Ono and colleagues. 20,26,27) Although extensive structural and theoretical studies on the structure of this base pair in a DNA oligomer have been performed, [28][29][30][31][32][33][34][35][36][37][38][39][40][41] the experimental structure of the T-Hg(II)-T base pair from NMR and Raman spectroscopy was recently reported 27,42) (see the chemical structure of the T-Hg(II)-T base pair for that shown within Fig. 1b).…”