Influences of cooperative hydrogen bonding economy on protein-nucleic acid complexation: Structure of unidecahydrated Inosine C5′-monophosphate and L-glutamine (2C₁₀H₁₃N₄O₈P · C₅H₁₀N₂O₃ · 11H₂O) cocrystal at atomic resolution

The crystal structure of a unidecahydrated co-complex between two Inosine 5′-monophosphate (IMP) and one L-glutamine has been determined at atomic resolution by X-ray crystallographic methods. The crystal belongs to the monoclinic space group P2₁ with cell dimensions a = 8.690(2), b = 21.900(3), c = 12.370(1) Å, and β = 110.59(3)°. This structure reveals the recognition mechanism of glutamine to the nucleotide through direct and water-mediated hydrogen bonds. The phosphate oxygen (O23) seems to prefer the nonspecific interaction with the functional sites of glutamine (NA· · ·O23 = 2.672, OH· · ·O23 = 3.063, OE· · ·O23 = 3.104 Å), whereas the bases prefer specific (N23· · ·O = 2.874 Å) bindings. But here no specific interaction has been observed at N17 and N27, which were observed in serine - IMP complex. However, the solvent mediated N17· · ·OW3· · ·N27 hydrogen bonds for stabilization of the stacked purine bases have been observed as in other aminoacid-nucleotide cocrystals. The striking habit of glutamine to occupy the nearly same region of the nueleotide cocrystal as was found in the serine - IMP complex through substantial replacement of free and bound water molecules, shows certainly the cooperative hydrogen bonding economy of water molecules.