Mechanism and structural dynamics of sulfur transfer during de novo [2Fe-2S] cluster assembly on ISCU2

Maturation of iron-sulfur proteins in eukaryotes is initiated in mitochondria by the core iron-sulfur cluster assembly (ISC) complex, consisting of the cysteine desulfurase sub-complex NFS1-ISD11-ACP1, the scaffold protein ISCU2, the electron donor ferredoxin FDX2, and frataxin, a protein dysfunctional in Friedreich's ataxia. The core ISC complex synthesizes [2Fe-2S] clusters de novo from Fe and a persulfide (SSH) bound at conserved cluster assembly site residues. Here, we elucidate the poorly understood Fe-dependent mechanism of persulfide transfer from cysteine desulfurase NFS1 to ISCU2. High-resolution cryo-EM structures obtained from anaerobically prepared samples provide snapshots that both visualize different stages of persulfide transfer from Cys381NFS1 to Cys138ISCU2 and clarify the molecular role of frataxin in optimally positioning assembly site residues for fast sulfur transfer. Biochemical analyses assign ISCU2 residues essential for sulfur transfer, and reveal that Cys138ISCU2 rapidly receives the persulfide without a detectable intermediate. Mössbauer spectroscopy assessing the Fe coordination of various sulfur transfer intermediates shows a dynamic equilibrium between pre- and post-sulfur-transfer states shifted by frataxin. Collectively, our study defines crucial mechanistic stages of physiological [2Fe-2S] cluster assembly and clarifies frataxin's molecular role in this fundamental process.

Evaluation of the uptake, storage and cell effects of nano-iron in enterocyte-like cell models

The therapy with nanocompounds is widely used to treat Fe deficiency and an emerging trend to inhibit tumor growth. The present work aims to address the management of different FeONP, comparing sucrose covered FeONP and Fe nanoparticles in the form of the ferritin with non-particulated inorganic Fe (II) by enterocytes-like colon cancer cell lines (Caco-2 and HT-29). Iron uptake results revealed significantly higher Fe incorporation in the case of nanoparticulated Fe, first in the form of FeONP and second in the form of ferritin with respect to inorganic Fe (II). Furthermore, the intracellular Fe fractionation, conducted by size exclusion chromatography coupled on line to inductively coupled plasma mass spectrometry (SEC-ICP-MS) showed a significant increase of the Fe-ferritin peak upon exposure of cells to the following compounds ferritin > FeONP > FeSO_4. Such results point out that the sucrose coated FeONP released Fe into the cell cytosol that was used to replenish the existing cytosolic ferritin without inducing changes in the protein concentration. On the other hand, the increase of the Fe-ferritin peak in cells exposed to ferritin as iron source is due to a significant increase on the intracellular protein concentration, as proved by using an ICP-MS linked ferritin sandwich immune assay. Cell viability experiments conducted with concentrations up to 1000 μmol L^-1 (as Fe) of each compound under scrutiny did not reveal significant differences among Fe species regarding global cellular toxicity. However, significant cell DNA damage was detected when treating the cells with FeONP (500 μmol L^-1).

Iron speciation, ferritin concentrations and Fe : ferritin ratios in different malignant breast cancer cell lines: on the search for cancer biomarkers

Iron is an essential element for cell growth and division. Recent experiments have linked a deregulation of iron's metabolism with breast cancer progression, aggressiveness and recurrence. In fact, it is conceived that chronic failure in the redox balance due to the presence of a high intracellular concentration of this metal has the potential to modulate specific signaling networks associated with cancer malignancy. Thus, this work has been focused on the comparative evaluation of part of the Fe metallome in two breast cancer cell lines of different malignancies: MCF-7 and MDA-MB-231. Evaluation of the total cytosolic iron content as well as the ultrafiltrable iron content has been conducted using inductively coupled plasma mass spectrometry (ICP-MS) as a Fe selective detector. The obtained results revealed a significantly higher total Fe concentration in the less malignant phenotype. Additionally, Fe-fractionation experiments, conducted by coupling size exclusion chromatography (SEC) to ICP-MS showed a similar Fe distribution (speciation) in both cell phenotypes. However, further specific ferritin measurement using immunochemical based ICP-MS assays showed important differences regarding the total protein content among cell lines and, most importantly, significant differences in the Fe-content of the ferritin molecules between cell lines. This finding points out an iron-storage independent function also associated with ferritin in the most malignant phenotype of the evaluated breast cancer cells that stresses the interest in this molecule as a cancer biomarker.

Atomic resolution studies detect new biologic evidences on the Turin Shroud

We performed reproducible atomic resolution Transmission Electron Microscopy and Wide Angle X-ray Scanning Microscopy experiments studying for the first time the nanoscale properties of a pristine fiber taken from the Turin Shroud. We found evidence of biologic nanoparticles of creatinine bounded with small nanoparticles of iron oxide. The kind, size and distribution of the iron oxide nanoparticles cannot be dye for painting but are ferrihydrate cores of ferritin. The consistent bound of ferritin iron to creatinine occurs in human organism in case of a severe polytrauma. Our results point out that at the nanoscale a scenario of violence is recorded in the funeral fabric and suggest an explanation for some contradictory results so far published.