Gas-phase conformations of deprotonated trinucleotides (dGTT-, dTGT-, and dTTG-):: The question of zwitterion formation
Gas-phase conformations of deprotonated trinucleotides (dGTT-, dTGT-, and dTTG-):: The question of zwitterion formation
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DOI：
10.1016/s1044-0305(02)00866-8
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发表时间：
2003-02-01
影响因子：
3.2
通讯作者：
Bowers, MT
中科院分区：
文献类型：
--
作者：
Gidden, J;Bowers, MT
研究了一系列含胸腺嘧啶（T）和鸟嘌呤（G）碱基的三核苷酸的气相构象，探讨了形成两性离子的可能性。通过MALDI形成去质子化的dGTT（-）、dTGT（-）和dTTG（-）离子，并且通过基于离子迁移率的方法测量它们在氦气中的碰撞截面。假设两性离子和非两性离子结构对dTGT-进行理论建模，而dGTT（-）和dTTG（-）被认为是“对照组”并且仅建模为非两性离子。在两性离子中，G在N7位点被质子化，并且两个相邻的磷酸被去质子化。在非两性离子中，G不被质子化，只有一个磷酸基团被去质子化。在80 K实验中，观察到dTGT-的两种构象，其横截面在圆（2）上相差17 +/- 2（A）。多个构象也观察到dGTT-和dTTG-在80 K，虽然构象之间的相对横截面差异不能准确地获得。在较高的温度下（>200 K），构象迅速相互转换的实验时间尺度和一个单一的“时间平均”构象中观察到的离子迁移率数据。理论预测只有一个低能量构象的两性离子形式的dTGT-与横截面比实验值小8%。此外，G上额外的H+不会桥接两个磷酸盐。因此，dTGT-在气相中似乎不是稳定的两性离子。然而，理论确实预测了dTGT的非两性离子形式的两种低能构象，其在圆（2）上的横截面相差18 +/- 3（A），与实验非常一致。在较小的横截面形式（折叠构象异构体）中，G和其中一个T碱基堆叠，而另一个T朝向堆叠对折叠并与G氢键结合。在较大的横截面形式（开放型构象异构体）中，未堆叠的T远离T/G堆叠对延伸。类似的折叠和开放构象预测所有三个三核苷酸，无论磷酸去质子化。（J Am Soc Mass Spectrom 2003，14，161 -170）（C）2003年美国质谱学会。
The gas-phase conformations of a series of trinucleotides containing thymine (T) and guanine (G) bases were investigated for the possibility of zwitterion formation. Deprotonated dGTT(-), dTGT(-), and dTTG(-) ions were formed by MALDI and their collision cross-sections in helium measured by ion mobility based methods. dTGT- was theoretically modeled assuming a zwitterionic and non-zwitterionic structure while dGTT(-) and dTTG(-) were considered "control groups" and modeled only as non-zwitterions. In the zwitterion, G is protonated at the N7 site and the two neighboring phosphates are deprotonated. In the non-zwitterion, G is not protonated and only one phosphate group is deprotonated. Two conformers, whose cross-sections differ by 17 +/- 2 (A) over circle (2), are observed for dTGT- in the 80 K experiments. Multiple conformers are also observed for dGTT- and dTTG- at 80 K, though relative cross-section differences between the conformers could not be accurately obtained. At higher temperatures (>200 K), the conformers rapidly interconvert on the experimental time scale and a single "time-averaged" conformer is observed in the ion mobility data. Theory predicts only one low-energy conformation for the zwitterionic form of dTGT- with a cross-section 8% smaller than experimental values. Additionally, the extra H+ on G does not bridge both phosphates. Thus, dTGT- does not appear to be a stable zwitterion in the gas-phase. Theory does, however, predict two low-energy conformers for the non-zwitterionic form of dTGT- that differ in cross-section by 18 +/- 3 (A) over circle (2), in good agreement with the experiment. In the smaller cross-section form (folded conformer), G and one of the T bases are stacked while the other T folds towards the stacked pair and hydrogen bonds to G. In the larger cross-section form (open conformer), the unstacked T extends away from the T/G stacked pair. Similar folded and open conformers are predicted for all three trinucleotides, regardless of which phosphate is deprotonated. (J Am Soc Mass Spectrom 2003,14,161-170) (C) 2003 American Society for Mass Spectrometry.