Influences of cooperative hydrogen bonding economy on protein-nucleic acidcomplexation: Structure of unidecahydrated Inosine C5 '-monophosphate and L-glutamine (2C(10)H(13)N(4)O(8)P center dot C5H10N2O3 center dot 11H(2)O) 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 res olution by X-ray crystallographic methods. The crystal belongs to the monoc linic space group P2(1) with cell dimensions a = 8.690(2), b = 21.900(3), c = 12.370(1) Angstrom, and beta = 110.59(3)degrees. 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 Angstrom), whereas the bases prefer specific (N23 ... O = 2.874 Angstrom) bindings. But here no sp ecific interaction has been observed at N17 and N27, which were observed in serine - IMP complex. However, the solvent mediated N17 ... OW3 ... N27 hy drogen bonds for stabilization of the stacked purine bases have been observ ed as in other aminoacid-nucleotide cocrystals. The striking habit of gluta mine to occupy the nearly same region of the nucleotide cocrystal as was fo und in the serine - IMP complex through substantial replacement of free and bound water molecules, shows certainly the cooperative hydrogen bonding ec onomy of water molecules.