title: Crystal structure of 3-(adenin-9-yl)propionhistamide hydrochloride monohydrate and the role of protonation in protein-nucleic acid interactions.
abstract: The three-dimensional structure of 3-(adenin-9-yl)propionhistamide hydrochloride, as a model of interactions between the protonated imidazolyl group and adenine moiety, has been determined by X-ray crystallography. The crystal data are a = 10.314 (1), b = 7.854 (1), c = 20.780 (1) A, beta = 92.765 (4), Z = 4, Dm = 1.32 g X cm-3, space group P2(1)/n. The imidazolium group interacts with adenine moiety by stacking. A comparison with the related neutral derivatives leads to a hypothesis that adenine stacks with the protonated, but not with the neutral, imidazolyl group. Such a characteristic behaviour of the imidazolyl group depending on protonation was shown by ultraviolet and NMR spectroscopy, and by polarographic experiments in solution. We note that a role of the essential histidine in RNAase reaction is a switch between capture and ejection of the substrate, which depends upon proton uptake and its release, respectively.
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives*; D004247:DNA; D006632:Histamine / Q000031:analogs & derivatives*; D006860:Hydrogen Bonding; D008954:Models, Biological; D008958:Models, Molecular; D008968:Molecular Conformation; D011485:Protein Binding; D011506:Proteins; D011687:Purines; D011743:Pyrimidines; D014961:X-Ray Diffraction
chemical_list: C040515:3-(adenin-9-yl)propionhistamide; D011506:Proteins; D011687:Purines; D011743:Pyrimidines; D006632:Histamine; D004247:DNA; D000225:Adenine