Zhang Zhaoying, Kim Seho, Gaffney Barbara L, Jones Roger A
Department of Chemistry and Chemical Biology, Rutgers-The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854, USA.
J Am Chem Soc. 2006 May 31;128(21):7015-24. doi: 10.1021/ja0613714.
Using UV, CD, and NMR, we demonstrate that the important bacterial signaling molecule involved in biofilm formation, cyclic diguanosine monophosphate (c-di-GMP), exists as a mixture of five different but related structures in an equilibrium that is sensitive both to its concentration and to the metal present. At the lower concentrations used for UV and CD work (0.05-0.5 mM), Li(+), Na(+), Cs(+), and Mg(2+) favor a bimolecular self-intercalated structure, while K(+), Rb(+), and NH(4)(+) favor formation of one or more guanine quartet complexes as well. At the higher NMR concentrations ( approximately 30 mM), the bimolecular structures associate and rearrange to a mixture of all-syn and all-anti tetramolecular and octamolecular quartet complexes. With K(+) the octamolecular complexes predominate, while with Li(+) the tetramolecular and octamolecular quartet complexes are present in approximately equal amounts, along with the bimolecular structure. We also find that both guanine amino groups in c-di-GMP are essential for formation of the quartets, because substitution of inosine for one guanosine allows formation of only the bimolecular structure. Further, two molecules of c-di-GMP tethered together are constrained in such a way that limits their ability to form these quartet complexes. The polymorphism we describe may provide different options for this signaling molecule when performing its functions in a bacterial cell, with K(+) and its own local concentration controlling the equilibrium.
通过紫外光谱（UV）、圆二色光谱（CD）和核磁共振（NMR），我们证明了参与生物膜形成的重要细菌信号分子环二鸟苷单磷酸（c-di-GMP）以五种不同但相关结构的混合物形式存在，处于一种对其浓度和存在的金属都敏感的平衡状态。在用于UV和CD研究的较低浓度（0.05 - 0.5 mM）下，Li⁺、Na⁺、Cs⁺和Mg²⁺有利于形成双分子自插层结构，而K⁺、Rb⁺和NH₄⁺则有利于形成一种或多种鸟嘌呤四重奏复合物。在较高的NMR浓度（约30 mM）下，双分子结构会缔合并重排为全顺式和全反式四分子和八分子四重奏复合物的混合物。对于K⁺而言，八分子复合物占主导，而对于Li⁺，四分子和八分子四重奏复合物以及双分子结构大致等量存在。我们还发现，c-di-GMP中的两个鸟嘌呤氨基对于四重奏的形成至关重要，因为用肌苷取代一个鸟苷仅能形成双分子结构。此外，两个连接在一起的c-di-GMP分子受到限制，从而限制了它们形成这些四重奏复合物的能力。我们所描述的多态性可能为这种信号分子在细菌细胞中发挥功能时提供不同的选择，其中K⁺及其局部浓度控制着平衡。
