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G E Norris

Publications and source records attributed to G E Norris.

23 records · Page 2Linked to original sources
PubMed1987

Spectrochemical studies on the blue copper protein azurin from Alcaligenes denitrificans.

Spectroscopic and electrochemical studies, incorporating electronic spectra, electron paramagnetic resonance (EPR) spectra, resonance Raman (RR) spectra, and measurements of the redox potential, have been carried out on the blue copper protein azurin, from Alcaligenes denitrificans. These data are correlated with the refined crystal structure of this azurin and with corresponding data for other blue copper proteins. The electronic spectrum, characterized by an intense (epsilon = 5100 M-1 cm-1) charge-transfer band at 619 nm, the EPR spectral parameters (g perpendicular = 2.059, g parallel of = 2.255, A parallel of = 60 X 10(-4) cm-1), and the resonance Raman spectrum are similar to those obtained from other azurins and from plastocyanins. Both the electronic spectrum and the EPR spectrum are unchanged over the pH range 4-10.5, but major changes occur above pH 12 and below pH 3.5. A small reversible change occurs at pH approximately 11.4. In the RR spectrum the Cu-S stretching mode is shown to contribute to all of the five principal RR peaks. Deuterium substitution produces shifts in at least seven of the peaks; these shifts may be attributable, at least in part, to the NH...S hydrogen bond to the copper-ligated Cys-112. Measurements of the redox potential, using spectroelectrochemical methods, over the temperature range 4.8-40.0 degrees C, give values for delta H0' and delta S0' of -55.6 kJ mol-1 and -97.0 J K-1 mol-1, respectively. The redox potential of A. denitrificans azurin at pH 7.0, Eo', is 276 mV. These data are interpreted in terms of a copper site, in azurin, comprising three strong bonds, in an approximately trigonal plane, from Cys-112, His-46, and His-117 and much longer axial approaches from Met-121 and the peptide carbonyl oxygen of Gly-45. Spectral differences within the azurin family and between azurin and plastocyanin are attributed to differences in the strengths of these axial interactions. Likewise, the distinctly lower Eo values for azurins, as compared with plastocyanins, are related to the more copper(II)-like site in azurin [with a weaker Cu-S(Met) interaction and a Cu-O interaction not found in plastocyanin]. On the other hand, the relative constancy of the EPR parameters between azurin and plastocyanin suggests they are not strongly influenced by weakly interacting axial groups.

Alcaligenes↗
PubMed1987

Structure of human lactoferrin at 3.2-A resolution.

The three-dimensional structure of human milk lactoferrin, a member of the transferrin family, has been determined crystallographically at 3.2-A resolution. The molecule has two-fold internal homology. The N- and C-terminal halves form two separate globular lobes, connected by a short alpha-helix, and carry one iron-binding site each. Each lobe has the same folding, based on two domains of similar supersecondary structure, with the iron site at the domain interface. Each iron atom is coordinated by four protein ligands: two tyrosines, one histidine, and one aspartate. A probable CO3(2-) (or HCO3-) ion is suggested by the electron density, bound to iron and adjacent to an arginine side chain and a helix N terminus. The protein folding and location of the binding sites show marked similarities with those of other binding proteins, notably the sulfate-binding protein from Salmonella typhimurium.

Binding Sites↗
PubMed1986

Preliminary crystallographic studies on bovine lactoferrin.

The purification of bovine lactoferrin, its crystallization at low ionic strength, and preliminary X-ray crystallographic data are reported. The crystals, which grow from a two-phase system, are radiation-stable and suitable for a medium-resolution X-ray analysis. They are orthorhombic, space group P2(1)2(1)2(1), with cell dimensions a = 138.4 A, b = 87.1 A, c = 73.6 A, and one protein molecule in the asymmetric unit.

Animals↗
PubMed1983

Structure of azurin from Alcaligenes denitrificans at 2.5 A resolution.

The structure of the blue copper protein, azurin, from Alcaligenes denitrificans has been determined from an electron density map at a nominal resolution of 3.0 A. Four isomorphous heavy-atom derivatives, prepared with KAu(CN)2, uranyl acetate, Hg(NH3)2Cl2 and KAu(CN)2 + uranyl acetate (a double derivative) were used to calculate phases by the method of isomorphous replacement. The overall figure of merit was 0.61. The two molecules in the asymmetric unit are related by an approximate 2-fold axis. Independent interpretations of the density were made for the two molecules, and the structures have since been partially refined. After 12 refinement cycles, using the Hendrickson-Konnert restrained least-squares program, the R factor is 0.318 for data to 2.5 A resolution and there are no major conformational differences between the two molecules. Refinement is continuing. Eight extended strands of the polypeptide chain form a beta-barrel structure whose topology is the same as that of plastocyanin and the alternative folding proposed for Pseudomonas aeruginosa azurin. As in the latter two proteins, the copper atom forms three short bonds, with His-46 N delta 1, His117 N delta 1 and Cys112 S gamma, and one longer bond, with Met121 S delta, these four ligands forming a very distorted tetrahedron. A possible additional interaction, between copper and the carbonyl oxygen of Gly45, cannot be discounted at the present stage of the analysis. A surface hydrophobic patch, around the edge of the imidazole ring of His117 appears the most likely electron transfer locus. The sequences of azurin and plastocyanin have been aligned and the homology between the two proteins is discussed.

Alcaligenes↗