Wong Alan, Wu Gang
Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6.
J Am Chem Soc. 2003 Nov 12;125(45):13895-905. doi: 10.1021/ja0302174.
We report a solid-state multinuclear ((23)Na, (15)N, (13)C, and (31)P) NMR study on the relative affinity of monovalent cations for a stacking G-quartet structure formed by guanosine 5'-monophosphate (5'-GMP) self-association at pH 8. Two major types of cations are bound to the 5'-GMP structure: one at the surface and the other within the channel cavity between two G-quartets. The channel cation is coordinated to eight carbonyl oxygen atoms from the guanine bases, whereas the surface cation is close to the phosphate group and likely to be only partially hydrated. On the basis of solid-state (23)Na NMR results from a series of ion titration experiments, we have obtained quantitative thermodynamic parameters concerning the relative cation binding affinity for each of the two major binding sites. For the channel cavity site, the values of the free energy difference (Delta G degrees at 25 degrees C) for ion competition between M(+) and Na(+) ions are K(+) (-1.9 kcal mol(-1)), NH(4)(+) (-1.8 kcal mol(-1)), Rb(+) (-0.3 kcal mol(-1)), and Cs(+) (1.8 kcal mol(-1)). For the surface site, the values Delta G degrees are K(+) (2.5 kcal mol(-1)), NH(4)(+) (-1.3 kcal mol(-1)), Rb(+) (1.1 kcal mol(-1)), and Cs(+) (0.9 kcal mol(-1)). Solid-state NMR data suggest that the affinity of monovalent cations for the 5'-GMP structure follows the order NH(4)(+) > Na(+) > Cs(+) > Rb(+) > K(+) at the surface site and K(+) > NH(4)(+) > Rb(+) > Na(+) > Cs(+) > Li(+) at the channel cavity site. We have found that the cation-induced stability of a 5'-GMP structure is determined only by the affinity of monovalent cations for the channel site and that the binding of monovalent cations to phosphate groups plays no role in 5'-GMP self-ordered structure. We have demonstrated that solid-state (23)Na and (15)N NMR can be used simultaneously to provide mutually complementary information about competitive binding between Na(+) and NH(4)(+) ions.
我们报道了一项关于单价阳离子对鸟苷 5'-单磷酸（5'-GMP）在 pH 8 时自缔合形成的堆积 G-四重奏结构相对亲和力的固态多核（（23）Na、（15）N、（13）C 和（31）P）核磁共振研究。有两种主要类型的阳离子与 5'-GMP 结构结合：一种在表面，另一种在两个 G-四重奏之间的通道腔内。通道阳离子与鸟嘌呤碱基的八个羰基氧原子配位，而表面阳离子靠近磷酸基团，可能仅部分水合。基于一系列离子滴定实验的固态（23）Na 核磁共振结果，我们获得了关于两种主要结合位点中每种位点相对阳离子结合亲和力的定量热力学参数。对于通道腔位点，M(+)与 Na(+)离子之间离子竞争的自由能差（25℃时的ΔG°）值为：K(+)（-1.9 kcal mol(-1)）、NH(4)(+)（-1.8 kcal mol(-1)）、Rb(+)（-0.3 kcal mol(-1)）和 Cs(+)（1.8 kcal mol(-1)）。对于表面位点，ΔG°值为：K(+)（2.5 kcal mol(-1)）、NH(4)(+)（-1.3 kcal mol(-1)）、Rb(+)（1.1 kcal mol(-1)）和 Cs(+)（0.9 kcal mol(-1)）。固态核磁共振数据表明，单价阳离子对 5'-GMP 结构的亲和力在表面位点遵循 NH(4)(+) > Na(+) > Cs(+) > Rb(+) > K(+)的顺序，在通道腔位点遵循 K(+) > NH(4)(+) > Rb(+) > Na(+) > Cs(+) > Li(+)的顺序。我们发现，5'-GMP 结构的阳离子诱导稳定性仅由单价阳离子对通道位点的亲和力决定，并且单价阳离子与磷酸基团的结合在 5'-GMP 自有序结构中不起作用。我们已经证明，固态（23）Na 和（15）N 核磁共振可以同时用于提供关于 Na(+)和 NH(4)(+)离子之间竞争结合的相互补充信息。
