title: The characterization of Thermotoga maritima ferritin reveals an unusual subunit dissociation behavior and efficient DNA protection from iron-mediated oxidative stress.
abstract: Ferritin from the hyperthermophilic anaerobe Thermotoga maritima, a bacterium of ancient phylogenetic origin, is structurally similar to known bacterial and eukaryotic ferritins: 24 identical subunits assemble into a shell having octahedral symmetry and a Mr of about 460 kDa. T. maritima ferritin (TmFtn), purified to homogeneity as a recombinant protein, contains approximately 2-3 iron atoms and can incorporate efficiently up to 3,500 atoms in the form of a ferric oxy-hydroxide mineral at 80°C, the optimal growth temperature of the bacterium. The 24-mer unexpectedly dissociates reversibly into dimers at low ionic strengths. In turn, dimers re-associate into the native 24-mer assembly at high protein concentrations and upon incorporation of iron micelles containing at least 500 Fe(III). TmFtn uses O(2) as efficient iron oxidant. The reaction stoichiometry is 3-4 O(2):Fe(II) as in all bacterial ferritins. Accordingly no H(2)O(2) is released into solution, a feature reflected in the in vitro ability of TmFtn to reduce significantly iron-mediated oxidative damage to DNA at 80°C. A similar TmFtn-mediated ROS detoxifying role likely occurs in the bacterium which lacks the SOD/catalase defense systems of the aerobic world.
authors.affiliation: Institute of Molecular Biology & Pathology, CNR, Rome, Italy. pierpaolo.ceci@uniroma1.it
authors.forename: Pierpaolo
authors.initials: P
authors.lastname: Ceci
authors.forename: Elena
authors.initials: E
authors.lastname: Forte
authors.forename: Gisa
authors.initials: G
authors.lastname: Di Cecca
authors.forename: Manuela
authors.initials: M
authors.lastname: Fornara
authors.forename: Emilia
authors.initials: E
authors.lastname: Chiancone
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D004249:DNA Damage; D004269:DNA, Bacterial / Q000378:metabolism*; D005293:Ferritins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D007501:Iron / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D017382:Reactive Oxygen Species / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D020124:Thermotoga maritima / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D021122:Protein Subunits; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D005293:Ferritins; D007501:Iron