Andrushchenko V V, van de Sande J H, Wieser H, Kornilova S V, Blagoi Y P
Department of Chemistry, Faculty of Science, University of Calgary, AB, Canada.
J Biomol Struct Dyn. 1999 Dec;17(3):545-60. doi: 10.1080/07391102.1999.10508385.
The B-Z transition of the synthetic oligonucleotide, (dG-dC)20, induced by Mn2+ ions at room temperature, was investigated by absorption and Vibrational Circular Dichroism (VCD) spectroscopy in the range of 1800-800 cm(-1). Metal ion concentration was varied from 0 to 0.73 M Mn2+ (0 to 8.5 moles of Mn2+ per mole of oligonucleotide phosphate, [Mn]/[P]). While both types of spectra showed considerable changes as the Mn2+ concentrations were raised, differences between the two were often complementary in their expression and extent, those displayed by VCD being more clearly evident due to the inversion of the opposite helical sense from the right-handed to the left-handed conformation. The main phase of the transition occurred in the metal ion concentration between 0.8-1.1 [Mn]/[P]. Gradual changes that took place in the spectra were interpreted in terms of simultaneous processes that depended on metal ion concentration, namely B-Z transformation, binding of Mn2+ to phosphates and to nitrogen bases, and partial denaturation. Below approximately 0.6 [Mn]/[P], only a small portion of the oligonucleotide adopted the Z conformation within a 3 hour period, whereas conversion was completed in the same time interval for concentrations between 0.9-1.2 [Mn]/[P]. At [Mn]/[P] >1.7, complete transition to the Z-form took place immediately on adding Mn2+. Applying VCD spectroscopy in combination with conventional infrared absorption proved most useful for corroborating changes in the absorption spectra, and for detecting in an unique manner, not attainable by absorption methods, conformational changes that lead to the inversion of the helical sense of the oligonucleotide.
在室温下，通过吸收光谱和振动圆二色性（VCD）光谱，在1800 - 800 cm⁻¹范围内研究了由Mn²⁺离子诱导的合成寡核苷酸（dG - dC）₂₀的B - Z转变。金属离子浓度在0至0.73 M Mn²⁺之间变化（每摩尔寡核苷酸磷酸有0至8.5摩尔Mn²⁺，[Mn]/[P]）。随着Mn²⁺浓度升高，两种光谱都显示出相当大的变化，但两者之间的差异在表达和程度上往往是互补的，由于从右手螺旋构象到左手螺旋构象的相反螺旋方向的反转，VCD显示的差异更明显。转变的主要阶段发生在金属离子浓度为0.8 - 1.1 [Mn]/[P]之间。光谱中发生的逐渐变化是根据依赖于金属离子浓度的同时进行的过程来解释的，即B - Z转变、Mn²⁺与磷酸盐和氮碱基的结合以及部分变性。在大约0.6 [Mn]/[P]以下，在3小时内只有一小部分寡核苷酸采用Z构象，而在0.9 - 1.2 [Mn]/[P]的浓度下，在相同的时间间隔内转变完成。在[Mn]/[P] > 1.7时，加入Mn²⁺后立即完全转变为Z型。将VCD光谱与传统红外吸收相结合被证明对于证实吸收光谱的变化以及以吸收方法无法实现的独特方式检测导致寡核苷酸螺旋方向反转的构象变化最为有用。
