The characterization of Thermotoga maritima ferritin reveals an unusual subunit dissociation behavior and efficient DNA protection from iron-mediated oxidative stress

• Published in: Extremophiles : life under extreme conditions 2011-05, Vol.15 (3), p.431-439
• Main Authors: Ceci, Pierpaolo, Forte, Elena, Di Cecca, Gisa, Fornara, Manuela, Chiancone, Emilia
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animal, plant and microbial ecology; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biochemistry; Biological and medical sciences; Biomedical and Life Sciences; Biotechnology; Cloning, Molecular; Crystallography, X-Ray; Deoxyribonucleic acid; DNA; DNA Damage; DNA, Bacterial - metabolism; Ferritins - chemistry; Ferritins - genetics; Ferritins - metabolism; Fundamental and applied biological sciences. Psychology; Hot Temperature; Hydrogen peroxide; Iron; Iron - metabolism; Life Sciences; Microbial Ecology; Microbiology; Models, Molecular; Molecular Sequence Data; Original Paper; Osmolar Concentration; Oxidation-Reduction; Oxidative Stress; Oxidizing agents; Protein Stability; Protein Structure, Quaternary; Protein Subunits; Reactive Oxygen Species - metabolism; Recombinant Proteins - metabolism; Space life sciences; Thermotoga maritima - genetics; Thermotoga maritima - metabolism
• ISSN: 1431-0651; 1433-4909
• DOI: 10.1007/s00792-011-0374-3

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.