Browsing by Author "Chiu, Wei-Chun"

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Crystal structure of Helicobacter pylori formamidase AmiF reveals a cysteine-glutamate-lysine catalytic triad
(2007-04-20)
Hung, Chiu-Lien
;
Liu, Jia-Hsin
;
Chiu, Wei-Chun
;
Huang, Shao-Wei
;
Hwang, Jenn-Kang
Helicobacter pylori AmiF formamidase that hydrolyzes formamide to produce formic acid and ammonia belongs to a member of the nitrilase superfamily. The crystal structure of AmiF was solved to 1.75 angstrom resolution using single-wavelength anomalous dispersion methods. The structure consists of a homohexamer related by 3-fold symmetry in which each subunit has an alpha-beta-beta-alpha four-layer architecture characteristic of the nitrilase superfamily. One exterior alpha layer faces the solvent, whereas the other one associates with that of the neighbor subunit, forming a tight alpha-beta-beta-alpha-alpha-beta-beta-alpha dimer. The apo and liganded crystal structures of an inactive mutant C166S were also determined to 2.50 and 2.30 angstrom, respectively. These structures reveal a small formamide-binding pocket that includes Cys(166), Glu(60), and Lys(133) catalytic residues, in which Cys166 acts as a nucleophile. Analysis of the liganded AmiF and N-carbamoyl D-amino acid amidohydrolase binding pockets reveals a common Cys-Glu-Lys triad, another conserved glutamate, and different subsets of ligand-binding residues. Molecular dynamic simulations show that the conserved triad has minimal fluctuations, catalyzing the hydrolysis of a specific nitrile or amide in the nitrilase superfamily efficiently.
Iron(III) Bound by Hydrosulfide Anion Ligands: NO-Promoted Stabilization of the [Fe-III-SH] Motif
(2014-07-02)
Tsou, Chih-Chin
;
Chiu, Wei-Chun
;
Ke, Chun-Hung
;
Tsai, Jia-Chun
;
Wang, Yun-Ming
Spontaneous transformation of the thermally stable [HS](-)bound {Fe(NO)(2)}(9) dinitrosyl iron complex (DNIC) [(HS)(2)Fe(NO)(2)](-) (1) into [(NO)(2)Fe(mu-S)](2)(2-) (Roussin's red salt (RRS)) along with release of H2S, probed by NBD-SCN (NBD = nitrobenzofurazan), was observed when DNIC 1 was dissolved in water at ambient temperature. The reversible transformation of RRS into DNIC 1 (RRS -> DNIC 1) in the presence of H2S was demonstrated. In contrast, the thermally unstable hydrosulfide-containing mononitrosyl iron complex (MNIC) [(HS)(3)Fe-III(NO)](-) (3) and [Fe-III(SH)(4)](-) (5) in THF/DMF spontaneously dimerized into the first structurally characterized Fe-III-hydrosulfide complexes [(NO)(SH)Fe(mu-S)](2)(2-) (4) with two {Fe(NO)}(7) motifs antiferromagnetically coupled and [(SH)(2)Fe(mu-S)](2)(2-) (6) resulting from two Fe-III (S = 5/2) centers antiferromagnetically coupled to yield an S = 0 ground state with thermal occupancy of higher spin states, respectively. That is, the greater the number of NO ligands bound to [2Fe2S], the larger the antiferromagnetic coupling constant. On the basis of DFT computation and the experimental (and calculated) reduction potential (E-1/2) of complexes 1, 3, and 5, the NO-coordinate ligand(s) of complexes 1 and 3 serves as the stronger electron-donating ligand, compared to thiolate, to reduce the effective nuclear charge (Z(eff)) of the iron center and prevent DNIC 1 from dimerization in an organic solvent (MeCN).
Iron(III) Bound by Hydrosulfide Anion Ligands: NO-Promoted Stabilization of the [Fe-III-SH] Motif
(2014-07-02)
Tsou, Chih-Chin
;
Chiu, Wei-Chun
;
Ke, Chun-Hung
;
Tsai, Jia-Chun
;
Wang, Yun-Ming
Spontaneous transformation of the thermally stable [HS](-)bound {Fe(NO)(2)}(9) dinitrosyl iron complex (DNIC) [(HS)(2)Fe(NO)(2)](-) (1) into [(NO)(2)Fe(mu-S)](2)(2-) (Roussin\'s red salt (RRS)) along with release of H2S, probed by NBD-SCN (NBD = nitrobenzofurazan), was observed when DNIC 1 was dissolved in water at ambient temperature. The reversible transformation of RRS into DNIC 1 (RRS -> DNIC 1) in the presence of H2S was demonstrated. In contrast, the thermally unstable hydrosulfide-containing mononitrosyl iron complex (MNIC) [(HS)(3)Fe-III(NO)](-) (3) and [Fe-III(SH)(4)](-) (5) in THF/DMF spontaneously dimerized into the first structurally characterized Fe-III-hydrosulfide complexes [(NO)(SH)Fe(mu-S)](2)(2-) (4) with two {Fe(NO)}(7) motifs antiferromagnetically coupled and [(SH)(2)Fe(mu-S)](2)(2-) (6) resulting from two Fe-III (S = 5/2) centers antiferromagnetically coupled to yield an S = 0 ground state with thermal occupancy of higher spin states, respectively. That is, the greater the number of NO ligands bound to [2Fe2S], the larger the antiferromagnetic coupling constant. On the basis of DFT computation and the experimental (and calculated) reduction potential (E-1/2) of complexes 1, 3, and 5, the NO-coordinate ligand(s) of complexes 1 and 3 serves as the stronger electron-donating ligand, compared to thiolate, to reduce the effective nuclear charge (Z(eff)) of the iron center and prevent DNIC 1 from dimerization in an organic solvent (MeCN).