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Biomedical subjects

C E Bugg

Publications and source records attributed to C E Bugg.

At least 73 records · Page 4Linked to original sources
PubMed1976

Interactions of hydrated metal ions with nucleotides: the crystal structure of barium adenosine 5'-monophosphate heptahydrate.

The crystal and molecular structure of barium adenosine 5'-monophosphate heptahydrate was determined from x-ray diffraction data. Crystals of barium adenosine 5'-monophosphate heptahydrate are monoclinic, space group C2, with a = 32.559(3), b = 6.969(3), c = 9.597(1) A, and beta = 100.31(1) degrees. Intensity data were collected with an automated diffractometer. The structure was solved by the heavy-atom method and refined by least-squares to R = 0.034. This structure provides an example of an outer-sphere metal-nucleotide complex, in which a completely hydrated metal ion interacts with the nucleotide only through water bridges. The barium ion is coordinated to eight water molecules, which form a slightly distorted square antiprism. Seven of the eight water molecules from the barium hydration shell are hydrogen bonded to phosphate groups; three of these water molecules are also hydrogen bonded to other suitable acceptor sites on the base and ribose moieties. The conformation about the glycosidic bond is anti, with chiCN = 69 degrees, and, as in most nucleotide structures, the conformation about the C(4')-C(5') bond is gauche-gauche. However, the ribose displays an unusual conformation (best described as C(4')-exo) not previously observed in crystal structures of nucleosides or nucleotides, other than 3',5'-cyclic nucleotides. It is possible that this unusual conformation is a consequence of the metal-water-nucleotide bridging interactions.

Adenosine Monophosphate↗
PubMed1975

Calcium-carbohydrate bridges composed of uncharged sugars. Structure of a hydrated calcium bromide complex of alpha-fucose.

X-ray diffraction data were used to determine the crystal structure of a hydrated CaBr2 complex of alpha-fucose, a common terminal sugar of oligosaccharide chains on glycoproteins. Crystals of C6H12O5-CaBr2-3H2O are orthorhombic, space group P212121, with A equals 14.360(2), B equals 12.896(3), and C equals 8.043(1) A. Intensity data for 1442 independent reflections were measured with an automated diffractometer. A trial structure, obtained by the heavy-atom method, was refined by least-squares to R equals 0.052. Ca-2+ is chelated by a pair of hydroxyl groups from each of tow symmetry-related fucose molecules and is coordinated to three water molecules. Thus the structure consists of hydrated fucose-calcium-fucose bridges. The bridge geometry, which is dictated by the coordination requirements of Ca-2+, is like that of other calcium-carbohydrate complexes. Our results indicate that calcium-fucose interactions can provide an effective, sterospecific mechanism for cross-linking carbo hydrate chains. Similar calcium-carbohydrate bridges may be involved in a variety of Ca-2+-dependent agglutination and adhesion processes.

Binding Sites↗
PubMed1975

Relationship between the mutagenic and base-stacking properties of halogenated uracil derivatives. The crystal structures of 5-chloro- and 5-bromouracil.

Three-dimensional X-ray diffraction data were used to determine the crystal structures of 5-chlorouracil and 5-bromouracil, two mutagenic pyrimidine analogs that can substitute for thymine in DNA. Crystals of the two compounds are nearly isostructural. The space group is P21/c, with a equals 8.450(6), b equals 6.842(3), c equals 11.072(16) angstrom, beta equals 123.53(19) degrees for 5-chlorouracil, and a equals 8.598(3), b equals 6.886(1), c equals 11.417(5) angstrom, beta equals 123.93(3) degrees for 5-bromouracil. Intensity data were collected with an automated diffractometer. The structures were refined by full-matrix least-squares to R equals 0.058 for 5-chlorouracil and R equals 0.027 for 5-bromouracil. The analogs from planar, hydrogen-bonded ribbons that are nearly identical to those found in the crystal structure of thymine monohydrate. As in many other structures of 5-halogenated uracil derivatives, the bases assume a stacking pattern that permits intimate contacts between the halogen substituents and the pyrimidine rings of adjacent bases. This stacking pattern involves halogen contacts that are significantly shorter than normal van der Waals interactions. The crystallographic results provide additional evidence that halogen substituents influence the stacking patterns of uracil derivatives, while exerting little direct effect on the hydrogen-bonding properties. The observed stacking patterns are consistent with the hypothesis that altered stacking interactions may account for the mis-pairing between 5-halogenated uracil bases and guanine residues within double-helical nucleic acids.

Bromouracil↗
PubMed1975

Crystal structures of azathioprine dihydrate and 6-methylmercaptopurine trihydrate.

The crystal and molecular structures of 6-methylmercaptopurine trihydrate and of azathioprine dihydrate were determined by the use of three-dimensional, X-ray, diffractometer data and were refined by least squares. Both molecules crystallize in the N(9)-H tautomer form, in contrast to the N(7)-H tautomer form found in crystals of 6-mercaptopurine. Unlike 6-mercaptopurine, or other thiopurines that have unsubstituted thio groups, the sulfur atoms of 6-methylmercaptopurine and azathioprine do not act as hydrogen-bond acceptors in the crystal structures. These two derivatives of 6-mercaptopurine assume a conformation in which the substituents on the sulfur atom are directed away from the imidazole moiety of the purine.

Azathioprine↗
PubMed1975

Calcium binding to D-glucuronate residues: crystal structure of a hydrated calcium bromide salt of D-glucuronic acid.

Three-dimensional X-ray diffraction data were used to determine the crystal structure of alpha-D-glucuronate CaBr times 3H20, a model system for investigating the factors involved in the binding of calcium ions to D-glucuronate residues of oligo-and poly-saccharides. Crystals of the salt are monoclinic, space group P21, having a = 6.410 (1), b = 10.784 (2), c = 8.879 (1) A, betta = 92.07 (1)degrees, and Z = 2. Instensity data for 1082 reflections were measured with an automated diffractometer. A trial structure, obtained by the heavy-atom method, was refined by least squares to R = 0.025. The absolute configuration was confirmed by anomalous-dispersion effects. An outstanding feature of the crystal packing is the interaction of D-glucuronate anions with calcium ions. The calcium ion is coordinated to three symmetry-related D-glucuronate anions and to two water molecules. The D-glucuronate anion binds calcium cations through three chelation sites: one that involves a carboxyl-oxygen atom combined with O-5; one that includes the second carboxyl-oxygen atom acting in concert with O-4, and one composed of the O-1-O-2 pair of hydroxyl groups.

Calcium↗
PubMed1973

Conformation of N6-methyladenine, a base involved in DNA modification: restriction processes.

Crystal structures of N(6),N(9)-dimethyladenine and N(6)-methyladenine hydrochloride were determined from three-dimensional x-ray diffraction data. The bases assume a conformation in which the N(6)-methyl group blocks one of the hydrogen-bonding sites normally used by adenine to form Watson-Crick pairs with thymine in double-helical DNA. When in this conformation, N(6)-methyladenine residues might alter the secondary structure of DNA. thereby preventing the scission of modified DNA's by restriction enzymes.

Adenine↗