Square pyramidal dialkoxo-bound monooxo-vanadium(V) complex and its behavior in solution.
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Crystallography, X-Ray↗
Biomedical subjects
M S Lah
Publications and source records attributed to M S Lah.
Three-dimensional framework constructed using nanometer-sized metallamacrocycle as a secondary building unit.
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Journal Article↗
Structure-function in Escherichia coli iron superoxide dismutase: comparisons with the manganese enzyme from Thermus thermophilus.
The crystal structure of dimeric Fe(III) superoxide dismutase (SOD) from Escherichia coli (3006 protein atoms, 2 irons, and 281 solvents) has been refined to an R of 0.184 using all observed data between 40.0 and 1.85 A (34,879 reflections). Features of this structure are compared with the refined structure of MnSOD from Thermus thermophilus. The coordination geometry at the Fe site is distorted trigonal bipyramidal, with axial ligands His26 and solvent (proposed to be OH-), and in-plane ligands His73, Asp156, and His160. Reduction of crystals to the Fe(II) state does not result in significant changes in metal-ligand geometry (R = 0.188 for data between 40.0 and 1.80 A). The arrangement of iron ligands in Fe(II) and Fe(III)SOD closely matches the Mn coordination found in MnSOD from T. thermophilus [Ludwig, M.L., Metzger, A.L., Pattridge, K.A., & Stallings, W.C. (1991) J. Mol. Biol. 219, 335-358]. Structures of the Fe(III) azide (40.0-1.8 A, R = 0.186) and Mn(III) azide (20.0-1.8 A, R = 0.179) complexes, reported here, reveal azide bound as a sixth ligand with distorted octahedral geometry at the metal; the in-plane ligand-Fe-ligand and ligand-Mn-ligand angles change by 20-30 degrees to coordinate azide as a sixth ligand. However, the positions of the distal azide nitrogens are different in the FeSOD and MnSOD complexes. The geometries of the Fe(III), Fe(II), and Fe(III)-azide species suggest a reaction mechanism for superoxide dismutation in which the metal alternates between five- and six-coordination. A reaction scheme in which the ligated solvent acts as a proton acceptor in the first half-reaction [formation of Fe(II) and oxygen] is consistent with the pH dependence of the kinetic parameters and spectroscopic properties of Fe superoxide dismutase.
Amino Acid Sequence↗
The mobile flavin of 4-OH benzoate hydroxylase.
Para-hydroxybenzoate hydroxylase inserts oxygen into substrates by means of the labile intermediate, flavin C(4a)-hydroperoxide. This reaction requires transient isolation of the flavin and substrate from the bulk solvent. Previous crystal structures have revealed the position of the substrate para-hydroxybenzoate during oxygenation but not how it enters the active site. In this study, enzyme structures with the flavin ring displaced relative to the protein were determined, and it was established that these or similar flavin conformations also occur in solution. Movement of the flavin appears to be essential for the translocation of substrates and products into the solvent-shielded active site during catalysis.
Benzoate 4-Monooxygenase↗
Crystal structures of mutant Pseudomonas aeruginosa p-hydroxybenzoate hydroxylases: the Tyr201Phe, Tyr385Phe, and Asn300Asp variants.
Structures of the mutant p-hydroxybenzoate hydroxylases, Tyr201Phe, Tyr385Phe, and Asn300Asp, each complexed with the substrate p-OHB have been determined by X-ray crystallography. Crystals of these three mutants of the Pseudomonas aeruginosa enzyme, which differs from the wild-type Pseudomonas fluorescens enzyme at two surface positions (228 and 249), were isomorphous with crystals of the wild-type P. fluorescens enzyme, allowing the mutant structures to be determined by model building and refinement, starting from the coordinates for the oxidized P. fluorescens PHBH-3,4-diOHB complex [Schreuder, H.A., van der Laan, J.M., Hol, W.G.J., & Drenth, J. (1988) J. Mol. Biol. 199, 637-648]. The R factors for the structures described here are: Tyr385Phe, 0.178 for data from 40.0 to 2.1 A; Tyr201Phe, 0.203 for data from 40.0 to 2.3 A; and Asn300Asp, 0.193 for data from 40.0 to 2.3 A. The functional effects of the Tyr201Phe and Tyr385Phe mutations, described earlier [Entsch, B., Palfey, B.A., Ballou, D.P., & Massey, V. (1991) J. Biol. Chem. 266, 17341-17349], were rationalized with the assumption that the mutations perturbed the hydrogen-bonding interactions of the tyrosine residues but caused no other changes in the enzyme structure. In agreement with these assumptions, the positions of the substrate, the flavin, and the modified residues are not altered in the Tyr385Phe and Tyr201Phe structures. In contrast, substitution of Asp for Asn at residue 300 has more profound effects on the enzyme structure. The side chain of Asp300 moves away from the flavin, disrupting the interactions of the carboxamide group with the flavin O(2) atom, and the alpha-helix H10 that begins at residue 297 is displaced, altering its dipole interactions with the flavin ring. The functional consequences of these changes in the enzyme structure and of the introduction of the carboxyl group at 300 are described and discussed in the accompanying paper (Palfey et al., 1994b).
4-Hydroxybenzoate-3-Monooxygenase↗
Structural characterization of the manganese(IV) Schiff-base complex MnIV(5-Cl-SALAHP)2.
Bis[3-(5-chlorosalicylideneamino)propanolato-O,N,O']manganes e(IV) methanol solvate, [Mn(C10H10ClNO2)2].CH3OH, Mr = 510.3, monoclinic, P2(1)/c, a = 11.949 (2), b = 7.530 (2), c = 25.777 (6) A, beta = 105.75 (2) degrees, V = 2232.4 (8) A3, Z = 4, Dx = 1.518 g cm-3, lambda(Mo K alpha) = 0.7107 A, mu = 7.98 cm-1, F(000) = 1502, T = 300 K, R = 0.0343, wR = 0.032 for 2113 unique reflections with (I) greater than 3 sigma(I). The title complex MnIV(5-Cl-SALAHP)2 [5-Cl-SALAHP = 3-(5-chlorosalicylideneamino)propanolato] displays a regular octahedral geometry. The 5-Cl-SALAHP ligand is tridentate, forming a meridional chelate with one phenolato oxygen (Mn-Oavg = 1.90 A), one alkoxide oxygen (Mn-Oavg = 1.85 A) and one imine nitrogen (Mn-Navg = 2.02 A) coordinated to the metal. Important angles described by the six atoms bound to manganese are all very close to either 180 or 90 degrees except the N-Mn-N angle which is 174.7 degrees. Previous studies have shown that MnIV(5-Cl-SALAHP)2 displays a rhombic EPR spectrum with well-resolved 55Mn hyperfine structure on gx, gy and gz. In contrast, Mn(SALADHP)2 [SALADHP = 2-methyl-2-(salicylideneamino)-1,3-propanediolato] shows a broad, ill-defined signal at g = 5.15 and a weak g = 2 component. The different spectral forms result from the extent of distortion of the MnIV octahedron. The reported structure is of potential importance to the understanding of the photosynthetic water-oxidizing system.
Chemical Phenomena↗