Fe2+ and phosphate interactions in bacterial ferritin from Azotobacter vinelandii.

Fe2+ binding to both apo- and holo- bacterial ferritin from Azotobacter vinelandii (AVBF) was measured as a function of pH under carefully controlled anaerobic conditions. Fe2+ binding to apo-AVBF is strongly pH dependent with 25 Fe2+ ions/apo-AVBF binding tightly at pH 5.5 and over 150 Fe2+/apo-AVBF at pH 9.0. Holo-AVBF gave a similar pH-dependent binding profile with over 400 Fe2+/AVBF binding at pH of 9.0. Proton release per Fe2+ bound to either AVBF protein increases with increasing pH until a total of about two protons are released at pH 9.0. These binding results are both qualitatively and quantitatively different from corresponding measurements (Jacobs et al., 1989) on apo- and holo- mammalian ferritin (MF) where less Fe2+ binds in both cases. The high level of Fe2+ binding to holo-AVBF relative to that of mammalian ferritin is a consequence of the higher phosphate content in the core of AVBF. Reduction of AVBF by either dithionite or methyl viologen in the absence of chelating agents demonstrated that phosphate, but not Fe2+, is released from the AVBF core in amounts commensurate with the degree of iron reduction, although even at 100% reduction considerable phosphate remains associated with the reduced mineral core. Fe2+ binding to holo-AVBF made deficient in phosphate was lower than that of native AVBF, while the addition of phosphate to native holo-AVBF increased the Fe2+ binding capacity. These results clearly support the role of phosphate as the site of interaction of Fe2+ with the AVBF mineral core.(ABSTRACT TRUNCATED AT 250 WORDS)     

Redox reactions of apo mammalian ferritin.

Apo horse spleen ferritin undergoes a 6.3 +/- 0.5 electron redox reaction at -310 mV at pH 6.0-8.5 and 25 degrees C to form reduced apoferritin (apoMFred). Reconstituted ferritin containing up to 50 ferric ions undergoes reduction at the same potential, taking up one electron per ferric ion and six additional electrons by the protein. We propose that apo mammalian ferritin (apoMF) contains six redox centers that can be fully oxidized forming oxidized apoferritin (apoMFox) or fully reduced forming apoMFred. ApoMFred can be prepared conveniently by dithionite or methyl viologen reduction. ApoMFred is slowly oxidized by molecular oxygen but more rapidly by Fe(CN)6(3-) to apoMFox. Fe(III)-cytochrome c readily oxidizes apoMFred to apoMFox with a stoichiometry of 6 Fe(III)-cytochrome c per apoMFred, demonstrating a rapid interprotein electron-transfer reaction. Both redox states of apoMF react with added Fe3+ and Fe2+. Addition of eight Fe2+ to apoMFox under anaerobic conditions produced apoMFred and Fe3+, as evidenced by the presence of a strong g = 4.3 EPR signal. Subsequent addition of bipyridyl produced at least six Fe(bipyd)3(2+) per MF, establishing the reversibility of this internal electron-transfer process between the redox centers of apoMF and bound iron. Incubation of apoMFred with the Fe(3+)-ATP complex under anaerobic conditions resulted in the formation and binding of two Fe2+ and four Fe3+ by the protein. The various redox states formed by the binding of Fe2+ and Fe3+ to apoMFox and apoMFred are proposed and discussed. The yellow color of apoMF appears to be an integral characteristic of the apoMF and is possibly associated with its redox activity.     

Structure of a ricin mutant showing rescue of activity by a noncatalytic residue.

Ricin A chain is an N-glycosidase which removes a single adenine base from a conservative loop of 28S rRNA, thereby inactivating eukaryotic ribosomes. The mechanism of action has been proposed to include transition-state stabilization of an oxycarbonium ion on the substrate ribose by interaction with Glu 177. Conversion of Glu 177 to Gln reduces activity nearly 200-fold [Ready, M. P., Kim, Y., & Robertus, J. D. (1991) Proteins: Struct., Funct., Genet. 10, 270-278] while conversion to Ala (E177A) reduces activity only 20-fold [Schlossman, D., Withers, D., Welsh, P., Alexander, A., Robertus, J., & Frankel, A. (1989) Mol. Cell. Biol. 9, 5012-5021]. X-ray analysis of the latter mutant protein shows that a residue at the edge of the active site, Glu 208, rotates into the space left vacant by the mutation. Its rearranged carboxylate partially substitutes for that of Glu 177. This is equivalent to the rescue of enzyme activity by a second-site reversion. Kinetic analysis shows the E177A mutation affects kcat and not Km, consistent with the notion that the carboxylate serves in transition-state stabilization.     

Genetics of intracisternal-A-particle-related envelope-encoding proviral elements in mice.

Intracisternal-A-particle-related envelope-encoding (IAPE) proviral elements in the mouse genome encode and express an envelope-like protein that may allow transmission of IAPEs as infectious agents. To test IAPE mobility and potential transmission in mice, we have analyzed the distribution of IAPE elements in the genomes of Mus spretus and Mus musculus inbred strains and wild-caught animals. Potential full-length (IAPE-A) proviral elements are present as repetitive copies in DNA from male but not female animals of M. musculus inbred strains and Mus musculus castaneus. Analysis of IAPE-cellular junction fragments indicates that fixation of most IAPEs in the germ line occurred in M. musculus and M. spretus after speciation but before M. musculus inbred strains were derived.     

Morphological variability of geographically distinct populations of the estuarine copepod Acartia Tonsa

Variations in the number of spines on the left and right posterior dorsal and posterior margins of the prosome as well as the length of the prosome of Acartia tonsa from three estuaries, the upper western side of the Chesapeake Bay, Montauk Bay near the eastern end of Long Island Sound and the coast of Peru were determined. The length of the prosome and number of spines in each of the four locations were used as an indication of morphological similarity between the populations.     

Copper association with iron sulfide magnetosomes in a magnetotactic bacterium

Greigite (Fe₃S₄) and pyrite (FeS₂) particles in the magnetosomes of a many-celled, magnetotactic prokaryote (MMP), common in brackish-to-marine, sulfidic, aquatic habitats, contained relatively high concentrations of copper which ranged from about 0.1 to 10 atomic per cent relative to iron. In contrast, the greigite particles in the magnetosomes of a curved magnetotactic bacterium collected from the same sampling site did not contain significant levels of copper. The ability of the MMP to biomineralize copper within its magnetosomes appeared to be limited to that organism and dependent upon the site from which it was collected. Although the chemical mechanism and physiological function of copper accumulation in the magnetosomes of the MMP is unclear, the presence of copper is the first evidence that another transition metal ion could be incorporated in the mineral phase of the magnetosomes of a magnetotactic bacterium.Abbreviation MMP many-celled magnetotactic prokaryote     

Change in climatically suitable breeding distributions reduces hybridization potential between Vermivora warblers

Aim

Climate change is affecting the distribution of species and subsequent biotic interactions, including hybridization potential. The imperiled Golden-winged Warbler (GWWA) competes and hybridizes with the Blue-winged Warbler (BWWA), which may threaten the persistence of GWWA due to introgression. We examined how climate change is likely to alter the breeding distributions and potential for hybridization between GWWA and BWWA.

Location

North America.

Methods

We used GWWA and BWWA occurrence data to model climatically suitable conditions under historical and future climate scenarios. Models were parameterized with 13 bioclimatic variables and 3 topographic variables. Using ensemble modeling, we estimated historical and modern distributions, as well as a projected distribution under six future climate scenarios. We quantified breeding distribution area, the position of and amount of overlap between GWWA and BWWA distributions under each climate scenario. We summarized the top explanatory variables in our model to predict environmental parameters of the distributions under future climate scenarios relative to historical climate.

Results

GWWA and BWWA distributions are projected to substantially change under future climate scenarios. GWWA are projected to undergo the greatest change; the area of climatically suitable breeding season conditions is expected to shift north to northwest; and range contraction is predicted in five out of six future climate scenarios. Climatically suitable conditions for BWWA decreased in four of the six future climate scenarios, while the distribution is projected to shift east. A reduction in overlapping distributions for GWWA and BWWA is projected under all six future climate scenarios.

Main Conclusions

Climate change is expected to substantially alter the area of climatically suitable conditions for GWWA and BWWA, with the southern portion of the current breeding ranges likely to become climatically unsuitable. However, interactions between BWWA and GWWA are expected to decline with the decrease in overlapping habitat, which may reduce the risk of genetic introgression.     

Selenium in combination with a tomato lipid extract as a therapy for benign prostatic hyperplasia and its alterations in rats with induced BPH

Benign prostatic hyperplasia (BPH) is the most common adenoma in old men. Tomatoes are a rich source of bioactive compounds that, as well as selenium (Se), possess antioxidant and antiproliferative activity. The aim was to evaluate the therapeutic effect of Se in combination with a tomato extract in aged rats with BPH. Aged male Wistar rats were divided in the following groups (n = 10 rats/group): Control (C), BPH, BPH + Finasteride (BPH + F), BPH + Tomato Lipidic Extract (BPH + E), BPH + Selenium (BPH + S) and BPH plus E plus S (BPH + E + S). After 4 weeks of treatment, prostate weight, diuresis, antioxidants enzymes, prooxidants and inflammatory markers, growth factors and androgens were determined. BPH + E + S reduced prostate weight by 59.29% and inhibited growth by 99.35% compared to BPH + F which only decreased weight and inhibited growth by 15.31% and 57.54%, respectively. Prooxidant markers were higher with BPH + F (49.4% higher vs. BPH), but BPH + E + S decreased these markers (94.27% vs. BPH) and increased antioxidant activity. Finally, diuresis was higher with the BPH + E + S combination and markers of inflammation and growth factors were significantly lower with respect to BPH + F. Our findings provide a beneficial and protective therapeutic option of E + S directed against androgens, oxidative stress and inflammation that regulates cell proliferation in the prostate gland.     

PYK2 is overexpressed in chronic lymphocytic leukaemia: A potential new therapeutic target

Chronic Lymphocytic Leukaemia (CLL) is the most common adult B-cell leukaemia and despite improvement in patients' outcome, following the use of targeted therapies, it remains incurable. CLL supportive microenvironment plays a key role in both CLL progression and drug resistance through signals that can be sensed by the main components of the focal adhesion complex, such as FAK and PYK2 kinases. Dysregulations of both kinases have been observed in several metastatic cancers, but their role in haematological malignancies is still poorly defined. We characterized FAK and PYK2 expression and observed that PYK2 expression is higher in leukaemic B cells and its overexpression significantly correlates with their malignant transformation. When targeting both FAK and PYK2 with the specific inhibitor defactinib, we observed a dose–response effect on CLL cells viability and survival. In vivo treatment of a CLL mouse model showed a decrease of the leukaemic clone in all the lymphoid organs along with a significant reduction of macrophages and of the spleen weight and size. Our results first define a possible prognostic value for PYK2 in CLL, and show that both FAK and PYK2 might become putative targets for both CLL and its microenvironment (e.g. macrophages), thus paving the way to an innovative therapeutic strategy.