c-di-GMP displays A monovalent metal ion-dependent polymorphism

Cyclic diguanosine monophosphate (c-di-GMP) is known to be an important signaling molecule that regulates the formation of bacterial biofilms. We demonstrate here by UV, CD, and NMR that it displays a surprising polymorphism that varies with the monovalent counterion and is consistent with the formation of a G-quartet structure in K⁺ and a stacked structure in Li⁺ or Na⁺. The ability of this rigid molecule to adopt different alignments may be important to its biological role.