Iron binding at specific sites within the octameric HbpS protects streptomycetes from iron-mediated oxidative stress.

The soil bacterium Streptomyces reticuli secretes the octameric protein HbpS that acts as a sensory component of the redox-signalling pathway HbpS-SenS-SenR. This system modulates a genetic response on iron- and haem-mediated oxidative stress. Moreover, HbpS alone provides this bacterium with a defence mechanism to the presence of high concentrations of iron ions and haem. While the protection against haem has been related to its haem-binding and haem-degrading activity, the interaction with iron has not been studied in detail. In this work, we biochemically analyzed the iron-binding activity of a set of generated HbpS mutant proteins and present evidence showing the involvement of one internal and two exposed D/EXXE motifs in binding of high quantities of ferrous iron, with the internal E78XXE81 displaying the tightest binding. We additionally show that HbpS is able to oxidize ferrous to ferric iron ions. Based on the crystal structure of both the wild-type and the mutant HbpS-D78XXD81, we conclude that the local arrangement of the side chains from the glutamates in E78XXE81 within the octameric assembly is a pre-requisite for interaction with iron. The data obtained led us to propose that the exposed and the internal motif build a highly specific route that is involved in the transport of high quantities of iron ions into the core of the HbpS octamer. Furthermore, physiological studies using Streptomyces transformants secreting either wild-type or HbpS mutant proteins and different redox-cycling compounds led us to conclude that the iron-sequestering activity of HbpS protects these soil bacteria from the hazardous side effects of peroxide- and iron-based oxidative stress.

Electrophysiological evidence of the effect of natural polyphenols upon the human higher brain functions.

OBJECTIVE: Several natural polyphenols exert effects upon the cardiovascular as well as nervous system. In vitro and animal studies suggest that polyphenols may potentially affect the human cognitive function. The aim was to study the effect of Provinols™, the polyphenolic compounds isolated from red wine, upon the human higher brain functions. MATERIAL AND METHODS: The accuracy of space memory was assessed by means of visually-guided and memory-guided saccadic eye movements. The EEG and blood pressure were registered also. The healthy undergraduates served as subjects. They were divided into the control, placebo and Provinols™ groups. The amplitudes of saccades, EEG spectral density, evoked potentials time-locked to saccadic onset and blood pressure were analyzed in control condition and 2 hours later, after administration of placebo, Provinols™ (4 mg/kg of body weight) or nothing. RESULTS: After the Provinols™ administration the memory-guided saccades were significantly more accurate and the significant decrease in the slow EEG bands, alpha power mainly, was registered over the broad regions of temporo-parietal cortex. No changes in saccadic eye movement related potentials as well as in blood pressure were found after the single dose Provinols™ administration. CONCLUSIONS: Even a single dose of the Provinols™ was able to affect positively the space memory for limited time duration. The improvement in space memory function and/or the positive role of attentional mechanisms may be taken into account mainly. More sensitive analysis of the particular participation of attentional and memory components demands the further study.

Molecular basis of hereditary iron homeostasis defects.

Iron is a trace element that is vital for life. It is a component of innumerable hemoproteins and many essential non-heme iron proteins that are involved in oxygen binding and metabolism and electron transfer. Nevertheless, iron can also be toxic to cells as it catalyses the production of oxygen radicals. Iron uptake, transport, storage and utilization are therefore strictly regulated to meet the body's iron needs and to avoid its potential toxicity. Any imbalance in iron homeostasis may lead to the development of pathological conditions associated with either iron overload or iron deficiency. In this paper, we review the current understanding of iron biology with a focus on erythroid iron demand. In addition, we will discuss molecular pathophysiology with implications for novel therapies of selected hereditary defects of iron homeostasis.

[Non-heme iron proteins as an alternative system of antioxidant defense in the cells of strictly anaerobic microorganisms: a review].

Enzymatic systems accounting for the relative oxygen resistance of multiple strict anaerobes are reviewed, with emphasis on molecular-biological properties and action mechanisms of non-heme iron proteins (neelaredoxins, desulfoferrodoxins, and rubrerythrins). These unique proteins, which are widespread in anaerobes, comprise a system of antioxidant defense against toxic effects of oxygen and products of its incomplete reduction (an alternative to the classic antioxidant system involving superoxide dismutase and catalase). The role of the superoxide reductase-mediated elimination of endogenous superoxide radicals is discussed. This extremely efficient means of rapid superoxide radical detoxification underlies the preferred mechanism for maintaining the optimum balance between oxidized and reduced forms of some proteins in the cells of strict anaerobes.

Memo-RhoA-mDia1 signaling controls microtubules, the actin network, and adhesion site formation in migrating cells.

Actin assembly at the cell front drives membrane protrusion and initiates the cell migration cycle. Microtubules (MTs) extend within forward protrusions to sustain cell polarity and promote adhesion site turnover. Memo is an effector of the ErbB2 receptor tyrosine kinase involved in breast carcinoma cell migration. However, its mechanism of action remained unknown. We report in this study that Memo controls ErbB2-regulated MT dynamics by altering the transition frequency between MT growth and shortening phases. Moreover, although Memo-depleted cells can assemble the Rac1-dependent actin meshwork and form lamellipodia, they show defective localization of lamellipodial markers such as alpha-actinin-1 and a reduced number of short-lived adhesion sites underlying the advancing edge of migrating cells. Finally, we demonstrate that Memo is required for the localization of the RhoA guanosine triphosphatase and its effector mDia1 to the plasma membrane and that Memo-RhoA-mDia1 signaling coordinates the organization of the lamellipodial actin network, adhesion site formation, and MT outgrowth within the cell leading edge to sustain cell motility.

Non-heme dioxygenases: cellular sensors and regulators jelly rolled into one?

Members of the Fe(II)- and 2-oxoglutarate-dependent family of dioxygenases have long been known to oxidize several amino acids in various protein targets to facilitate protein folding. However, in recent years investigators have characterized several such hydroxylation modifications that serve a regulatory, rather than structural, purpose. Furthermore, the responsible enzymes seem to function directly as sensors of the cellular environment and metabolic state. For example, a cellular response pathway to low oxygen (hypoxia) is orchestrated through the actions of prolyl and asparaginyl hydroxylases that govern both the oxygen-dependent stability and transcriptional activity of the hypoxia-inducible transcription factor. Recently, a different subfamily of Fe(II)- and 2-oxoglutarate-dependent dioxygenases has been shown to carry out histone demethylation. The discovery of protein regulation via hydroxylation raises the possibility that other Fe(II)- and 2-oxoglutarate-dependent dioxygenases might also serve in a similar capacity.

Omega oxygenases: nonheme-iron enzymes and P450 cytochromes.

Enzymes that effect with ease one of the most difficult chemical reactions, hydroxylation of an unfunctionalized alkyl group, are of particular interest because highly reactive intermediates must be produced. A typical example, the hydroxylation of fatty acids in the omega position, is now known to occur widely in nature. The catalysts, which can be called "omega-oxygenases," also insert molecular oxygen into a variety of other substrates at positions removed from activating functional groups, as in steroids, eicosanoids, and numerous drugs and other xenobiotics. Progress in the characterization of bacterial nonheme-iron enzymes, and plant, bacterial, and mammalian P450 cytochromes that catalyze fatty acid omega-oxidation, and evidence for multiple functional oxidants are summarized.

Recombinant human hepcidin expressed in Escherichia coli isolates as an iron containing protein.

Hepcidin is a small peptide that acts as a regulator of systemic iron homeostasis. To study some of its functional properties, a synthetic cDNA for the minimal, 20-amino-acid, form of human hepcidin was cloned into different constructs for expression in Escherichia coli. The fusion ferritin-hepcidin produced molecules retaining most of ferritin structural and functional properties, including ferroxidase and iron incorporation activities. However, it showed spectroscopic properties compatible with the presence of iron-sulfur complexes on the hepcidin moiety, which was buried into protein cavity. Similar complexes were reconstituted by in vitro incubation of the iron-free protein with iron and sulfide salts. Two other unrelated fusion products were constructed, which, when expressed in E. coli, formed insoluble aggregates retaining a large proportion of total bacterial iron. Analysis of the solubilized preparations showed them to contain iron-sulfur complexes. We concluded that the cysteine-rich hepcidin acts as an iron-sequestering molecule during expression in E. coli. This may have implications for the biological functions of this key protein of iron metabolism.