Electrochemical reduction of ferrous alpha-verdoheme in complex with heme oxygenase-1

The heme oxygenase (HO) reaction consists of three successive oxygenation reactions, i.e. heme to alpha-hydroxyheme, alpha-hydroxyheme to verdoheme, and verdoheme to biliverdin-iron chelate. Of these, the least understood step is the conversion of verdoheme to biliverdin-iron chelate. For the cleavage of the oxaporphyrin ring of ferrous verdoheme, involvement of a verdoheme pi-neutral radical has been proposed. To probe this hypothetical mechanism in the HO reaction, we performed electrochemical reduction of ferrous verdoheme complexed with rat HO-1 under anaerobic conditions. On the basis of the electrochemical spectral changes, the midpoint potential for the one-electron reduction of the oxaporphyrin ring of ferrous verdoheme was found to be -0.47+/-0.01 V vs the normal hydrogen electrode (NHE). Because this potential is far lower than those of both flavins of NADPH-cytochrome P450 reductase, and of NADPH, it is concluded that the one-electron reduction of the oxaporphyrin ring of ferrous verdoheme is unlikely to occur and that the formation of the pi-neutral radical cannot be the initial step in the degradation of verdoheme by HO. Rather, it appears more reasonable to consider an alternative mechanism in which binding of O(2) to the ferrous iron of verdoheme is the first step in the degradation of verdoheme.     

The crystal structure of a virus-like particle from the hyperthermophilic archaeon Pyrococcus furiosus provides insight into the evolution of viruses

Pyrococcus furiosus is a hyperthermophilic archaeal microorganism found near deep-sea thermal vents and its optimal growth temperature of 100 degrees C. Recently, a 38.8-kDa protein from P. furiosus DSM 3638 was isolated and characterized. Electron microscopy revealed that this protein aggregated as spheres of approximately 30 nm in diameter, which we designated P. furiosus virus-like particles (PfVs). X-ray crystallographic analysis at 3.6-A resolution revealed that each PfV consisted of 180 copies of the 38.8-kDa protein and retained T=3 icosahedral symmetry, as is often the case in spherical viruses. The total molecular mass of each particle was approximately 7 MDa. An examination of capsid structures suggested strong evolutionary links among PfV, tailed double-stranded DNA bacteriophages, and herpes viruses. The similar three-dimensional structures of the various coat proteins indicate that these viral capsids might have originated and evolved from a common ancestor. The structure of PfV provides a previously undescribed example of viral relationships across the three domains of life (Eukarya, Bacteria, and Archaea).     

Concerning the dynamic instability of actin homolog ParM

Apoptosis is a highly conserved procedure of cell death and occurs under various stimuli, including oxidative stress. A small heat shock protein, alphaB-crystallin, is found to process resistance to apoptosis in some cells and tissues. But the mechanisms under this protective role are not fully understood. In the present study, we reported the early protective role of alphaB-crystallin against hydrogen peroxide-induced apoptosis in mice myogenic C(2)C(12) cells. alphaB-Crystallin interacted with p53, a proapoptotic protein, during cell apoptosis and such protein interaction mainly occurred in the cytoplasm of the cells, suggesting that the interaction of alphaB-crystallin with p53 might prevent the translocation of p53 from cytoplasm to mitochondria. Hence, this study provides a hint that alphaB-crystallin affects on p53 mitochondrial translocation during oxidative stress-induced apoptosis.     

X-ray crystallographic and biochemical characterization of the inhibitory action of an imidazole-dioxolane compound on heme oxygenase

Heme oxygenase (HO) catalyzes the regiospecific cleavage of the porphyrin ring of heme using reducing equivalents and O2 to produce biliverdin, iron, and CO. Because CO has a cytoprotective effect through the p38-MAPK pathway, HO is a potential therapeutic target in cancer. In fact, inhibition of the HO isoform HO-1 reduces Kaposi sarcoma tumor growth. Imidazole-dioxolane compounds have recently attracted attention because they have been reported to specifically inhibit HO-1, but not HO-2, unlike Cr-containing protoporphyrin IX, a classical inhibitor of HO, that inhibits not only both HO isoforms but also other hemoproteins. The inhibitory mechanism of imidazole-dioxolane compounds, however, has not yet been characterized. Here, we determine the crystal structure of the ternary complex of rat HO-1, heme, and an imidazole-dioxolane compound, 2-[2-(4-chlorophenyl)ethyl]-2-[(1H-imidazol-1-yl)methyl]-1,3-dioxolane. This compound bound on the distal side of the heme iron, where the imidazole and 4-chlorophenyl groups were bound to the heme iron and the hydrophobic cavity in HO, respectively. Binding of the bulky inhibitor in the narrow distal pocket shifted the distal helix to open the distal site and moved both the heme and the proximal helix. Furthermore, the biochemical characterization revealed that the catalytic reactions of both HO-1 and HO-2 were completely stopped after the formation of verdoheme in the presence of the imidazole-dioxolane compound. This result should be mainly due to the lower reactivity of the inhibitor-bound verdoheme with O2 compared to the reactivity of the inhibitor-bound heme with O2.     

Enhancement of lipid peroxidation and its amelioration by vitamin E in a subject with mutations in the SBP2 gene

Selenocysteine (Sec) insertion sequence-binding protein 2 (SBP2) is essential for the biosynthesis of Sec-containing proteins, termed selenoproteins. Subjects with mutations in the SBP2 gene have decreased levels of several selenoproteins, resulting in a complex phenotype. Selenoproteins play a significant role in antioxidative defense, and deficiencies in these proteins can lead to increased oxidative stress. However, lipid peroxidation and the effects of antioxidants in subjects with SBP2 gene mutations have not been studied. In the present study, we evaluated the lipid peroxidation products in the blood of a subject (the proband) with mutations in the SBP2 gene. We found that the proband had higher levels of free radical-mediated lipid peroxidation products, such as 7β-hydroxycholesterol, than the control subjects. Treatment of the proband with vitamin E (α-tocopherol acetate, 100 mg/day), a lipid-soluble antioxidant, for 2 years reduced lipid peroxidation product levels to those of control subjects. Withdrawal of vitamin E treatment for 7 months resulted in an increase in lipid peroxidation products. Collectively, these results clearly indicate that free radical-mediated oxidative stress is increased in the subject with SBP2 gene mutations and that vitamin E treatment effectively inhibits the generation of lipid peroxidation products.