Regiospecificity of nucleotide-amino acid mating vs. water dynamics: a keyto protein-nucleic acid assemblies: structure of unidecahydrated inosine-5'-monophosphate and L-glutamic acid (2C(10)H(13)N(4)O(8)P center dot C5H11NO4 center dot 11H(2)O) cocrystal at atomic resolution

The crystal structure of a unidecahydrated cocomplex between two Inosine-5' -monophosphates (IMP) and one L-glutamic acid has been determined by X-ray crystallographic methods. The crystal belongs to the monoclinic space group P2(1) with cell dimensions a = 8.650(1), b = 21.900(1), c = 12.370(1) Angs trom and beta = 110.4 degrees (9). This structure reveals extensive hydroge n bonding of glutamic acid to the nucleotide through direct and water-media ted interactions. The phosphate oxygens (O3B and O1B) seem to prefer nonspe cific interaction with the functional sites of glutamic acid (OE2......O1B = 1.78 Angstrom, NA......O3B = 2.73 Angstrom, OH......O3B = 3.06 Angstrom), whereas the bases prefer specific (O...... N3B = 2.88 Angstrom) binding. A solvent mediated N7A...W5...N7B hydrogen bond used for stabilization of th e stacked purine bases has been observed as in other amino acid-nucleotide cocrystals. Glutamic acid occupies the same hydrophilic region in the nucle otide cocrystal as was found in glutamine-inosine monophosphate (Gln-IMP) a nd in serine-inosine monophosphate (Ser-IMP) complexes through substantial replacement of free and bound water molecules. This points to the dynamic h ydrogen bonding nature of the water molecules and their stereochemical coop eration for the placement of amino acid through the polycoordination within the crystal.