DNA Binding to Crystalline Silica Characterized by Fourier-Transform Infrared Spectroscopy

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DNA Binding to Crystalline Silica Characterized by

Fourier-Transform Infrared Spectroscopy

Yan Mao,1 Lambert N. ,1 Noel Whittaker,2 and

Umberto Saffiotti1

1Laboratory of Experimental Pathology, National Cancer

Institute, National Institutes of Health, Bethesda,

land;

2Laboratory of Analytical Chemistry, National

Institute of Diabetes and Digestive and Kidney

Diseases, National Institutes of Health, Bethesda,

land

Abstract

The interaction of DNA with crystalline silica in

buffered aqueous solutions at physiologic pH has been

investigated by Fourier-transform infrared

spectroscopy (FT-IR). In aqueous buffer, significant

changes occur in the spectra of DNA and silica upon

coincubation, suggesting that a DNA-silica complex

forms as silica interacts with DNA. As compared to the

spectrum of silica alone, the changes in the FT-IR

spectrum of silica in the DNA-silica complex are

consistent with an Si--O bond perturbation on the

surface of the silica crystal. DNA remains in a B-form

conformation in the DNA-silica complex. The most

prominent changes in the DNA spectrum occur in the

1225 to 1000 cm-1 region. Upon binding, the PO2-

asymmetric stretch at 1225 cm-1 is increased in

intensity and slightly shifted to lower frequencies;

the PO2- symmetric stretch at 1086 cm-1 is markedly

increased in intensity; and the band at 1053 cm-1,

representing either the phosphodiester or the C--O

stretch of DNA backbone, is significantly reduced in

intensity. In D2O buffer, the DNA spectrum reveals a

marked increase in intensity of the peak at 1086 cm-1

and a progressive decrease in intensity of the peak at

1053 cm-1 when DNA is exposed to increasing

concentrations of silica. The carbonyl band at 1688

cm-1 diminishes and shifts to slightly lower

frequencies with increasing concentrations of silica.

The present study demonstrates that crystalline silica

binds to the phosphate-sugar backbone of DNA. The

close proximity of the silica surface to the DNA

molecule, brought about by this binding, may

contribute to DNA strand breakage produced by

silica-derived free radicals. The ability of silica to

form stable complexes with DNA may play an important

role in the mechanisms of silica-induced toxicity and

carcinogenesis. -- Environ Health Perspect 102(Suppl

10):165-171 (1994)

Key words: silica, DNA adducts, Fourier-transform

infrared spectroscopy, silicosis, carcinogenesis

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