The iron superoxide dismutase from the filamentous cyanobacterium Nostoc PCC 7120. Localization, overexpression, and biochemical characterization.
The nitrogen-fixing filamentous cyanobacterium Nostoc PCC 7120 (formerly named Anabaena PCC 7120) possesses two genes for superoxide dismutase, a unique membrane-associated manganese superoxide dismutase (MnSOD) and a soluble iron superoxide dismutase (FeSOD). A phylogenetic analysis of FeSODs shows that cyanobacterial enzymes form a well separated cluster with filamentous species found in one subcluster and unicellular species in the other. Activity staining, inhibition patterns, and immunogold labeling show that FeSOD is localized in the cytosol of vegetative cells and heterocysts (nitrogenase containing specialized cells formed during nitrogen-limiting conditions). The recombinant Nostoc FeSOD is a homodimeric, acidic enzyme exhibiting the characteristic iron peak at 350 nm in its ferric state, an almost 100% occupancy of iron per subunit, a specific activity using the ferricytochrome assay of (2040 +/- 90) units mg(-1) at pH 7.8, and a dissociation constant Kd of the azide-FeSOD complex of 2.1 mM. Using stopped flow spectroscopy it was shown that the decay of superoxide in the presence of various FeSOD concentrations is first-order in enzyme concentration allowing the calculation of the catalytic rate constants, which increase with decreasing pH: 5.3 x 10(9) M(-1) s(-1) (pH 7) to 4.8 x 10(6) M(-1) s(-1) (pH 10). FeSOD and MnSOD complement each other to keep the superoxide level low in Nostoc PCC 7120, which is discussed with respect to the fact that Nostoc PCC 7120 exhibits oxygenic photosynthesis and oxygen-dependent respiration within a single prokaryotic cell and also has the ability to form differentiated cells under nitrogen-limiting conditions.
Regelsberger
Günther
G
Department of Chemistry, Division of Biochemistry, Metalloprotein Research Group, BOKU, University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.
Laaha
Ulrike
U
Dietmann
Dagmar
D
Rüker
Florian
F
Canini
Antonella
A
Grilli-Caiola
Maria
M
Furtmüller
Paul Georg
PG
Jakopitsch
Christa
C
Peschek
Günter A
GA
Obinger
Christian
C
D000595:Amino Acid Sequence; D018407:Bacterial Physiological Phenomena; D002462:Cell Membrane / Q000378:metabolism; D000458:Cyanobacteria / Q000201:enzymology*; D003600:Cytosol / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D008854:Microscopy, Electron; D008954:Models, Biological; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism; D010802:Phylogeny; D011506:Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D019810:Sodium Azide / Q000494:pharmacology; D013053:Spectrophotometry; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
D011506:Proteins; D011994:Recombinant Proteins; D019810:Sodium Azide; D006861:Hydrogen Peroxide; D007501:Iron; D013482:Superoxide Dismutase; D009584:Nitrogen