Ligand Binding to Chlorite Dismutase from Magnetospirillum sp.
Chlorite dismutase (Cld) catalyzes the reduction of chlorite to chloride and dioxygen. Here, the ligand binding to Cld of Magnetospirillum sp. (MaCld) is investigated with X-ray crystallography and electron paramagnetic resonance (EPR). EPR reveals a large heterogeneity in the structure of wild-type MaCld, showing a variety of low- and high-spin ferric heme forms. Addition of an axial ligand, such as azide or imidazole, removes this heterogeneity almost entirely. This is in line with the two high resolution crystal structures of MaCld obtained in the presence of azide and thiocyanate that show the coordination of the ligands to the heme iron. The crystal structure of the MaCld-azide complex reveals a single well-defined orientation of the azide molecule in the heme pocket. EPR shows, however, a pH-dependent heme structure, probably due to acid-base transitions of the surrounding amino-acid residues stabilizing azide. For the azide and imidazole complex of MaCld, the hyperfine and nuclear quadrupole interactions with the close-by (14)N and (1)H nuclei are determined using pulsed EPR. These values are compared to the corresponding data for the low-spin forms observed in the ferric wild-type MaCld and to existing EPR data on azide and imidazole complexes of other heme proteins.
BIMEF Laboratory, Department of Physics, University of Antwerp , Universiteitsplein 1, B-2610 Wilrijk, Belgium.
Amy
A
De Schutter
UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , 2829-516 Caparica, Portugal.
Hugo D
HD
Correia
UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , 2829-516 Caparica, Portugal.
Diana M
DM
Freire
Departamento de Física, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral , Ciudad Universitaria, Paraje El Pozo, S3000ZAA Santa Fe, Argentina.
María G
MG
Rivas
Departamento de Física, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral , Ciudad Universitaria, Paraje El Pozo, S3000ZAA Santa Fe, Argentina.
Alberto
A
Rizzi
UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , 2829-516 Caparica, Portugal.
Teresa
T
Santos-Silva
Departamento de Física, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral , Ciudad Universitaria, Paraje El Pozo, S3000ZAA Santa Fe, Argentina.
Pablo J
PJ
González
BIMEF Laboratory, Department of Physics, University of Antwerp , Universiteitsplein 1, B-2610 Wilrijk, Belgium.
Sabine
S
Van Doorslaer
D001386:Azides / Q000737:chemistry*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry*; D008024:Ligands; D042201:Magnetospirillum / Q000201:enzymology*; D008958:Models, Molecular; D010088:Oxidoreductases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D013861:Thiocyanates / Q000737:chemistry*
D001386:Azides; D007093:Imidazoles; D008024:Ligands; D013861:Thiocyanates; D010088:Oxidoreductases; C402794:chlorite dismutase; C031760:thiocyanate