Initial iron oxidation in horse spleen apoferritin. Characterization of a mixed-valence iron(II)-iron(III) complex.

In ferritin, iron is stored by oxidative deposition of the ferrous ion to form a hydrous ferric oxide mineral core. Two intermediates, formed during the initial stages of iron accumulation in apoferritin, have been observed previously in our laboratory and have been identified as a mononuclear Fe3(+)-protein complex and a mixed-valence Fe2(+)-Fe3(+)-protein complex. The physical characteristics of the mixed-valence Fe2(+)-Fe3+ complex and its relationship to the mononuclear Fe3+ complex in horse spleen apoferritin samples to which 0-240 iron atoms were added was examined by EPR spectroscopy. The results indicate that the mononuclear complex is not a precursor to the formation of the mixed-valence complex. Competitive binding studies with Cd2+, Zn2+, Tb3+, and UO2+(2) suggest that the mixed-valence complex is formed on the interior of the protein in the vicinity of the 2-fold axis of the subunit dimer. The mixed-valence complex could be generated by the partial oxidation of Fe2+ in apoferritin containing 120 Fe2+ or by the addition of up to 120 Fe2+ to ferritin already containing 18 Fe3+/protein molecule. The fact that the complex is generated during early Fe2+ oxidation suggests that it may be a key intermediate during the initial oxidative deposition of iron in the protein. The unusual EPR powder lineshape at 9.3 GHz of the mixed-valence complex was simulated with a rhombic g-tensor (gx = 1.95, gy = 1.88, gz = 1.77) and large linewidths and g-strain parameters. The presence of significant g-strain in the complex probably accounts for the failure to observe an EPR signal at 35 GHz and likely reflect considerable flexibility in the structure of the metal site. The temperature dependence of the EPR intensity in the range 8-38 K was modeled successfully by an effective spin Hamiltonian including exchange coupling (-2JS1.S2) and zero-field terms, from which an antiferromagnetic coupling of J = -4.0 +/- 0.5 cm-1 was obtained. This low value for J may reflect the presence of a mu-oxo bridge(s) in the dimer.     

The Heat-Resistant Agglutinin Family Includes a Novel Adhesin from Enteroaggregative Escherichia coli Strain 60A

Heat-resistant agglutinin 1 (Hra1) is an accessory colonization factor of enteroaggregative Escherichia coli (EAEC) strain 042. Tia, a close homolog of Hra1, is an invasin and adhesin that has been described in enterotoxigenic E. coli. We devised a PCR-restriction fragment length polymorphism screen for the associated genes and found that they occur among 55 (36.7%) of the enteroaggregative E. coli isolates screened, as well as lower proportions of enterotoxigenic, enteropathogenic, enterohemorrhagic, and commensal E. coli isolates. Overall, 25%, 8%, and 3% of 150 EAEC strains harbored hra1 alone, tia alone, or both genes, respectively. One EAEC isolate, 60A, produced an amplicon with a unique restriction profile, distinct from those of hra1 and tia. We cloned and sequenced the full-length agglutinin gene from strain 60A and have designated it hra2. The hra2 gene was not detected in any of 257 diarrheagenic E. coli isolates in our collection but is present in the genome of Salmonella enterica serovar Heidelberg strain SL476. The cloned hra2 gene from strain 60A, which encodes a predicted amino acid sequence that is 64% identical to that of Hra1 and 68% identical to that of Tia, was sufficient to confer adherence on E. coli K-12. We constructed an hra2 deletion mutant of EAEC strain 60A. The mutant was deficient in adherence but not autoaggregation or invasion, pointing to a functional distinction from the autoagglutinin Hra1 and the Tia invasin. Hra1, Tia, and the novel accessory adhesin Hra2 are members of a family of integral outer membrane proteins that confer different colonization-associated phenotypes.     

Hyperosmolarity enhanced susceptibility to renal tubular fibrosis by modulating catabolism of type I transforming growth factor‐β receptors

Hyperosmolarity plays an essential role in the pathogenesis of diabetic tubular fibrosis. However, the mechanism of the involvement of hyperosmolarity remains unclear. In this study, mannitol was used to evaluate the effects of hyperosmolarity on a renal distal tubule cell line (MDCK). We investigated transforming growth factor‐β receptors and their downstream fibrogenic signal proteins. We show that hyperosmolarity significantly enhances the susceptibility to exogenous transforming growth factor (TGF)‐β1, as mannitol (27.5 mM) significantly enhanced the TGF‐β1‐induced increase in fibronectin levels compared with control experiments (5.5 mM). Specifically, hyperosmolarity induced tyrosine phosphorylation on TGF‐β RII at 336 residues in a time (0–24 h) and dose (5.5–38.5 mM) dependent manner. In addition, hyperosmolarity increased the level of TGF‐β RI in a dose‐ and time‐course dependent manner. These observations may be closely related to decreased catabolism of TGF‐β RI. Hyperosmolarity significantly downregulated the expression of an inhibitory Smad (Smad7), decreased the level of Smurf 1, and reduced ubiquitination of TGF‐β RI. In addition, through the use of cycloheximide and the proteasome inhibitor MG132, we showed that hyperosmolarity significantly increased the half‐life and inhibited the protein level of TGF‐β RI by polyubiquitination and proteasomal degradation. Taken together, our data suggest that hyperosmolarity enhances cellular susceptibility to renal tubular fibrosis by activating the Smad7 pathway and increasing the stability of type I TGF‐β receptors by retarding proteasomal degradation of TGF‐β RI. This study clarifies the mechanism underlying hyperosmotic‐induced renal fibrosis in renal distal tubule cells. J. Cell. Biochem. 109: 663–671, 2010. © 2010 Wiley‐Liss, Inc.     

Fossil bananas (Musaceae): Ensete oregonense sp. nov. from the Eocene of western North America and its phytogeographic significance

Fossil seeds of Ensete, a genus presently native to Asia and Africa, have been recovered from the middle Eocene of Oregon, confirming the presence of Musaceae in the North American Tertiary. The seed of Ensete oregonense sp. nov. is operculate, with a well-defined micropylar collar, a pronounced chalazal chamber, and a wide hilar cavity. A survey of seed morphology in extant Zingiberales provides characters for distinguishing Musaceae from other families of the order, furnishes criteria for distinguishing the three extant genera of Musaceae (Musa, Ensete and Musella), and facilitates critical assessment of fossil seed remains. “Musa” cardiosperma Jain from the Cretaceous/Tertiary boundary Deccan Series of India is excluded from Musaceae (although retained in Zingiberales) on the basis of fruit and seed characters, including the lack of laticifers and absence of a chalazal chamber. We reexamined the musaceous seeds from Colombia that previously were described as Tertiary fossils (Musa enseteformis Berry, 1925) and now believe that they are recent, nonfossil remains, evidently from Ensete ventricosum, which is grown in the region where the specimens were originally obtained. In addition, a reputed fossil banana fruit from the Cretaceous of Colombia was reexamined and determined to be a concretion of nonbiological origin. Ensete oregonense is significant therefore, as the first unequivocal fossil record of Ensete and of Musaceae. Although the Musaceae are currently native only to the Old World tropics, this discovery establishes that the family was present in North America about 43 million years ago.     

Effects of initial maltose concentration, agitation and aeration rates on the production of glucosyltransferase byAspergillus niger CCRC 31494

Summary The microorganism Aspergillus niger CCRC 31494 can produce an extracellular glucosyltransferase (GTase, EC 2.4.1.24) with a high transglucosylating activity. The maximal enzyme production occurred at initial maltose concentration of 40 gl^-1. The microorganism was also grown in a 5-liter jar fermenter for GTase production. It was found that the optimal agitation and aeration rates were 750 rev min^-1 and 1.0 l min^-1, respectively, and the enzyme production was about 0.25–0.26 units ml^-1.     

Laboratory and field assessment of molluscicidal activity of B-2 against Oncomelania hupensis, the vector snail of schistosomiasis in China

Molluscicidal activity of B-2 (sodium 2,5-dichloro-4-bromophenol; called as Phebrol and registered in WHO as OMS 3012) was evaluated in a laboratory and the field trials were performed in two different localities in Yueyang city, China, for control of Oncomelania hupensis. B-2 was effective against O. hupensis both in the laboratory and in the field. A dosage of 50 g/m2 in 10% granular form or 20 ml/m2 in 25% liquid form of B-2 would be recommendable as a standard mollusciciding dose for control of O. hupensis.