Wan Cuihong, Guo Xinhua, Liu Zhiqiang, Liu Shuying
Changchun Center of Mass Spectrometry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, P. R. China.
J Mass Spectrom. 2008 Feb;43(2):164-72. doi: 10.1002/jms.1277.
Formation and stabilities of four 14-mer intermolecular DNA triplexes, consisting of third strands with repeating sequence CTCT, CCTT, CTT, or TTT, were studied by electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) in the gas phase. The gas-phase stabilities of the triplexes were compared with their CD spectra and melting behaviors in solution, and parallel correlation between two phases were obtained. In the presence of 20 mM NH(4) (+) (pH 5.5), the formation of the TTT triplex was not detected in both solution and the gas phase. Other triplexes showed the same order, CTCT > CCTT > CTT, of ion abundances in mass spectra and T(m) values in solution. The more stable triplexes are those that contained higher percentage of C(+).GC triplets and an alternating CT sequence. However, the CCTT with the same C(+).GC triplets as the CTCT showed a higher stability than the latter during the gas-phase dissociation. Furthermore, a biphasic triplex-to-duplex-to-single transition was detected in the gas phase, while a monophasic triplex-to-single dissociation was observed in solution. The present results reveal that hydrogen bonds and electrostatic interactions dominate in the gas phase, while base stacking and hydrophobic interactions dominate in solution to stabilize the triplexes. Moreover, weak acidic conditions (pH 5-6) promote the formation of the parallel triplexes.
采用电喷雾电离傅里叶变换离子回旋共振质谱（ESI-FTICR-MS）在气相中研究了四种由重复序列CTCT、CCTT、CTT或TTT的第三链组成的14聚体分子间DNA三链体的形成及其稳定性。将三链体在气相中的稳定性与其在溶液中的圆二色光谱（CD）和熔解行为进行了比较，并获得了两相之间的平行相关性。在20 mM NH(4) (+)（pH 5.5）存在的情况下，在溶液和气相中均未检测到TTT三链体的形成。其他三链体在质谱中的离子丰度顺序和在溶液中的熔解温度（T(m)）值顺序相同，即CTCT > CCTT > CTT。更稳定的三链体是那些含有较高百分比C(+).GC三联体和交替CT序列的三链体。然而，具有与CTCT相同C(+).GC三联体的CCTT在气相解离过程中显示出比后者更高的稳定性。此外，在气相中检测到三链体到双链体再到单链的双相转变，而在溶液中观察到三链体到单链的单相解离。目前的结果表明，在气相中氢键和静电相互作用起主导作用，而在溶液中碱基堆积和疏水相互作用起主导作用以稳定三链体。此外，弱酸性条件（pH 5-6）促进平行三链体的形成。
