Helix−Coil Transition of DNA Monitored by Pressure Perturbation Calorimetry

Abstract

We report the first use of pressure perturbation calorimetry (PPC) to characterize the heat-induced helix-coil transition of DNA polymers. The alternating copolymer poly[d(A-T)] was studied in aqueous solutions containing 5.2 and 18.2 mM Na+; it exhibited helix-coil transition temperatures of 33.6 and 44.7 degrees C, respectively. The transition is accompanied by a negative molar volume change, DeltaV) -2.6 and -2.1 mL/mol (base pair), respectively, and an increase in the coefficient of thermal expansion, Deltaalpha=+5x10(-4) K(-1) (at both ionic strengths). These values are consistent with a greater hydration of the coil form. The larger water-accessible surface area of the coil causes more water molecules to assume a bound, more densely packed structure that then gradually decreases with increasing temperature, leading to a larger value of R. The magnitude of the volume changes detected by PPC were larger than those deduced from high-pressure UV spectroscopy, shedding light on the effect of pressure on DeltaV. The shape of the PPC peak was nearly identical to the shape of the DSC peak, providing direct evidence for the correlation between the molar volume change and enthalpy change for the helix to coil transition of DNA.

Modulation of the Thermodynamic Signatures of an RNA Thermometer by Osmolytes and Salts

“…Zuschriften data ( Figure 3B)which is due to the different approximations applied. [19] At temperatures below around 319 K, we found the 4U RNAt ob eu nstable against pressurization, but becomes resistant to pressure stress at higher temperatures.In the presence of TMAO, the slope of DV o u T ðÞ ,t hat is, DE o u ,i s unchanged, but more positive DV o u values are observed. In contrast, the addition of 2 m urea leads to an increase of DE o u , most likely due to al arger partial expansibility of the unfolded state.…”

Characterization of DNA with an 8-oxoguanine modification

“…Integration and analysis (52) of these peaks yielded unfolding volumes (Δ V U ) of −28 cm 3 /mol (ODN-3) and −13 cm 3 /mol (ODN-4), revealing volume contractions of the system as the temperature is increased. If the existence of voids is considered negligible, these volume contractions reflect changes in the hydration state of the ODNs (50,51), i.e. ODN unfolding is accompanied by a decrease in its volume of hydration.…”

Probing volumetric properties of biomolecular systems by pressure perturbation calorimetry (PPC) – The effects of hydration, cosolvents and crowding

“…For example, the helix-to-coil transition of poly[d(A-T)] is accompanied by a negative molar volume change, DV % À2 mL/mol (base pair), and an increase in the coefficient of thermal expansion, Da = +5 Â 10 À4 K À1 [66]. These values are consistent with a markedly greater hydration of the coil form.…”

“…Pressure perturbation calorimetry has also been used recently to characterize the heat-induced helix-coil transition of DNA polymers [14,66]. For example, the helix-to-coil transition of poly[d(A-T)] is accompanied by a negative molar volume change, DV % À2 mL/mol (base pair), and an increase in the coefficient of thermal expansion, Da = +5 Â 10 À4 K À1 [66].…”