Oxido-reduction is not the only mechanism allowing ions to traverse the ferritin protein shell

Background

Most models for ferritin iron release are based on reduction and chelation of iron. However, newer models showing direct Fe(III) chelation from ferritin have been proposed. Fe(III) chelation reactions are facilitated by gated pores that regulate the opening and closing of the channels.

Scope of review

Results suggest that iron core reduction releases hydroxide and phosphate ions that exit the ferritin interior to compensate for the negative charge of the incoming electrons. Additionally, chloride ions are pumped into ferritin during the reduction process as part of a charge balance reaction. The mechanism of anion import or export is not known but is a natural process because phosphate is a native component of the iron mineral core and non-native anions have been incorporated into ferritin in vitro. Anion transfer across the ferritin protein shell conflicts with spin probe studies showing that anions are not easily incorporated into ferritin. To accommodate both of these observations, ferritin must possess a mechanism that selects specific anions for transport into or out of ferritin. Recently, a gated pore mechanism to open the 3-fold channels was proposed and might explain how anions and chelators can penetrate the protein shell for binding or for direct chelation of iron.

Conclusions and general significance

These proposed mechanisms are used to evaluate three in vivo iron release models based on (1) equilibrium between ferritin iron and cytosolic iron, (2) iron release by degradation of ferritin in the lysosome, and (3) metallo-chaperone mediated iron release from ferritin.     

Dissecting drug and vehicle metabolic effects in rats by a metabonomic approach

A combined application of high resolution (1)H NMR spectroscopy and multivariate statistical techniques focused on establishing a consistent statistical approach to metabonomic studies was tested. The data reduction, which is preliminary to the application of multivariate analysis to NMR spectra, was carried out by means of two complementary methods: pure Pattern Recognition (PR) and Assigned Signal Analysis (ASA). The simultaneous use of both approaches allowed us to obtain additional information in the analysis of metabonomic data, compared to the use of PR alone. This additional information consists in the possibility of a biochemical interpretation of the effects induced by treatment with xenobiotics, such as drugs or drug vehicles, on the metabolic networks of the systems under investigation. This approach allowed us to ascertain that a single-dose treatment with ST1959 vehicled by Sesame oil affects the production of hepatic glucose associated to an increment of the amino acid ketogenic process.     

Comparison of proteomes in various human plasma preparations by two-dimensional gel electrophoresis

Serum or plasma can be utilized in a variety of studies targeted toward the discovery of disease biomarkers. In this study, the proteome profiles of plasma samples prepared using various anticoagulants (EDTA, heparin or citrate), were compared with those of serum using two-dimensional electrophoresis (2-DE). Proteins which evidenced different levels in the plasma and serum were screened and identified using ESI-Q-TOF MS/MS. The proteins which became detectable after the removal of fibrinogen from serum were identified as pigment epithelial differentiating factor (four spots), fetuin-like protein, and the hemopexin precursor. In particular, three proteins, pre-serum amyloid P component, plasma glutathione peroxidase precursor, and tetranectin, evidenced increased volume intensity only in the plasma samples prepared with EDTA.     

Design of disulfide-linked thioredoxin dimers and multimers through analysis of crystal contacts

Disulfide bonds play an important role in protein stability and function. Here, we describe a general procedure for generating disulfide-linked dimers and multimers of proteins of known crystal structures. An algorithm was developed to predict sites in a protein compatible with intermolecular disulfide formation with neighboring molecules in the crystal lattice. A database analysis was carried out on 46 PDB coordinates to verify the general applicability of this algorithm to predict intermolecular disulfide linkages. On the basis of the predictions from this algorithm, mutants were constructed and characterized for a model protein, thioredoxin. Of the five mutants, as predicted, in solution four formed disulfide-linked dimers while one formed polymers. Thermal and chemical denaturation studies on these mutant thioredoxins showed that three of the four dimeric mutants had similar stability to wild-type thioredoxin while one had lower stability. Three of the mutant dimers crystallized readily (in four to seven days) in contrast to the wild-type protein, which is particularly difficult to crystallize and takes more than a month to form diffraction-quality crystals. In two of the three cases, the structure of the dimer was exactly as predicted by the algorithm, while in the third case the relative orientation of the monomers in the dimer was different from the predicted one. This methodology can be used to enhance protein crystallizability, modulate the oligomerization state and to produce linear chains or ordered three-dimensional protein arrays.     

Discovery of a thermophilic protein complex stabilized by topologically interlinked chains

A growing number of organisms have been discovered inhabiting extreme environments, including temperatures in excess of 100 degrees C. How cellular proteins from such organisms retain their native folds under extreme conditions is still not fully understood. Recent computational and structural studies have identified disulfide bonding as an important mechanism for stabilizing intracellular proteins in certain thermophilic microbes. Here, we present the first proteomic analysis of intracellular disulfide bonding in the hyperthermophilic archaeon Pyrobaculum aerophilum. Our study reveals that the utilization of disulfide bonds extends beyond individual proteins to include many protein-protein complexes. We report the 1.6 A crystal structure of one such complex, a citrate synthase homodimer. The structure contains two intramolecular disulfide bonds, one per subunit, which result in the cyclization of each protein chain in such a way that the two chains are topologically interlinked, rendering them inseparable. This unusual feature emphasizes the variety and sophistication of the molecular mechanisms that can be achieved by evolution.     

Herbivory-induced glucose transporter gene expression in the brown planthopper,Nilaparvata lugens

Nilaparvata lugens, the brown planthopper (BPH) feeds on rice phloem sap, containing high amounts of sucrose as a carbon source. Nutrients such as sugars in the digestive tract are incorporated into the body cavity via transporters with substrate selectivity. Eighteen sugar transporter genes of BPH (Nlst) were reported and three transporters have been functionally characterized. However, individual characteristics of NlST members associated with sugar transport remain poorly understood. Comparative gene expression analyses using oligo-microarray and quantitative RT-PCR revealed that the sugar transporter gene Nlst16 was markedly up-regulated during BPH feeding. Expression of Nlst16 was induced 2 h after BPH feeding on rice plants. Nlst16, mainly expressed in the midgut, appears to be involved in carbohydrate incorporation from the gut cavity into the hemolymph. Nlst1 (NlHT1), the most highly expressed sugar transporter gene in the midgut was not up-regulated during BPH feeding. The biochemical function of NlST16 was shown as facilitative glucose transport along gradients. Glucose uptake activity by NlST16 was higher than that of NlST1 in the Xenopus oocyte expression system. At least two NlST members are responsible for glucose uptake in the BPH midgut, suggesting that the midgut of BPH is equipped with various types of transporters having diversified manner for sugar uptake.     

Akt signalling in health and disease

Akt (also known as protein kinase B or PKB) comprises three closely related isoforms Akt1, Akt2 and Akt3 (or PKBα/β/γ respectively). We have a very good understanding of the mechanisms by which Akt isoforms are activated by growth factors and other extracellular stimuli as well as by oncogenic mutations in key upstream regulatory proteins including Ras, PI3-kinase subunits and PTEN. There are also an ever increasing number of Akt substrates being identified that play a role in the regulation of the diverse array of biological effects of activated Akt; this includes the regulation of cell proliferation, survival and metabolism. Dysregulation of Akt leads to diseases of major unmet medical need such as cancer, diabetes, cardiovascular and neurological diseases. As a result there has been substantial investment in the development of small molecular Akt inhibitors that act competitively with ATP or phospholipid binding, or allosterically. In this review we will briefly discuss our current understanding of how Akt isoforms are regulated, the substrate proteins they phosphorylate and how this integrates with the role of Akt in disease. We will furthermore discuss the types of Akt inhibitors that have been developed and are in clinical trials for human cancer, as well as speculate on potential on-target toxicities, such as disturbances of heart and vascular function, metabolism, memory and mood, which should be monitored very carefully during clinical trial.     

牡丹PsCS基因的克隆及序列分析

以牡丹品种‘赵粉’(Paeonia suffruticosa L.cv.‘Zhao Fen’)为试材,采用RT-PCR和RACE方法从雄蕊中获得了一个牡丹柠檬酸合成醇(citrate synthase,CS)基因cDNA全长,命名为PsCS,GenBank登录号为HQ449568.其cDNA全长1 564 bp,包含75 bp的5’非编码区、73 bp的3 '非编码区和一个长度为1 416 bp编码471个氨基酸的开放阅读框.序列比对和系统进化分析表明,PsCS与葡萄的亲缘关系最近,相似性达89.4％以上.     

The beneficial effect of aluminium and the role of citrate in Al accumulation in Melastoma malabathricum

* Here we investigated the beneficial effect of aluminium (Al) on the development of the Al accumulating plant Melastoma malabathricum. * Seedlings of M. malabathricum were cultivated in a nutrient solution containing 0.5 mM Al and compared with barley (Hordeum vulgare). In addition, roots of M. malabathricum were divided into one part growing in a nutrient solution, and the other part growing in a calcium solution. Al (0.5 mM) was applied to either solution. * Al-induced improvements of the root activity contributed to a growth enhancement in M. malabathricum. Al exposure without nutrients did not increase root growth and Al accumulation in the leaves. The beneficial effect, however, was induced by the combination of Al and nutrients. * We suggest that without nutrients roots are not able to synthesize an adequate amount of citrate that is required for transporting Al to the leaves. High Al levels in the plant tissues and/or an interaction of Al with particular nutrient elements in the apoplast of root cells appear to be essential to exert the beneficial effect of Al.