Spectral [corrected] studies on the cadmium-ion-binding properties of bovine brain S-100b protein

Heavy Metals and Essential Metals Are Associated with Cerebrospinal Fluid Biomarkers of Alzheimer's Disease

Various metals have been associated with the pathogenesis of Alzheimer's disease (AD), principally heavy metals that are environmental pollutants (such as As, Cd, Hg, and Pb) and essential metals whose homeostasis is disturbed in AD (such as Cu, Fe, and Zn). Although there is evidence of the involvement of these metals in AD, further research is needed on their mechanisms of toxicity. To further assess the involvement of heavy and essential metals in AD pathogenesis, we compared cerebrospinal fluid (CSF) AD biomarkers to macro- and microelements measured in CSF and plasma. We tested if macro- and microelements' concentrations (heavy metals (As, Cd, Hg, Ni, Pb, and Tl), essential metals (Na, Mg, K, Ca, Fe, Co, Mn, Cu, Zn, and Mo), essential non-metals (B, P, S, and Se), and other non-essential metals (Al, Ba, Li, and Sr)) are associated with CSF AD biomarkers that reflect pathological changes in the AD brain (amyloid β1-42, total tau, phosphorylated tau isoforms, NFL, S100B, VILIP-1, YKL-40, PAPP-A, and albumin). We used inductively coupled plasma mass spectroscopy (ICP-MS) to determine macro- and microelements in CSF and plasma, and enzyme-linked immunosorbent assays (ELISA) to determine protein biomarkers of AD in CSF. This study included 193 participants (124 with AD, 50 with mild cognitive impairment, and 19 healthy controls). Simple correlation, as well as machine learning algorithms (redescription mining and principal component analysis (PCA)), demonstrated that levels of heavy metals (As, Cd, Hg, Ni, Pb, and Tl), essential metals (Ca, Co, Cu, Fe, Mg, Mn, Mo, Na, K, and Zn), and essential non-metals (P, S, and Se) are positively associated with CSF phosphorylated tau isoforms, VILIP-1, S100B, NFL, and YKL-40 in AD.

Cadmium inhibitory action leads to changes in structure of ferredoxin:NADP(+) oxidoreductase

This study deals with the influence of cadmium on the structure and function of ferredoxin:NADP(+) oxidoreductase (FNR), one of the key photosynthetic enzymes. We describe changes in the secondary and tertiary structure of the enzyme upon the action of metal ions using circular dichroism measurements, Fourier transform infrared spectroscopy and fluorometry, both steady-state and time resolved. The decrease in FNR activity corresponds to a gentle unfolding of the protein, caused mostly by a nonspecific binding of metal ions to multiple sites all over the enzyme molecule. The final inhibition event is most probably related to a bond created between cadmium and cysteine in close proximity to the FNR active center. As a result, the flavin cofactor is released. The cadmium effect is compared to changes related to ionic strength and other ions known to interact with cysteine. The complete molecular mechanism of FNR inhibition by heavy metals is discussed.Electronic supplementary material The online version of this article (doi:10.1007/s10867-012-9262-z) contains supplementary material, which is available to authorized users.

Cadmium exposure modifies lactotrophs activity associated to genomic and morphological changes in rat pituitary anterior lobe

Cadmium (Cd) is widely used in industrial applications and is an important contaminant of agricultural products. As an endocrine disruptor, Cd modifies the hormone release of pituitary anterior lobe (PAL). This work was undertaken to evaluate a possible association between phospholipase D (PLD) and prolactin mRNA expressions and the activity of lactotrophs and folliculostellate cells (FSC) in PAL of Cd exposed adult male Wistar rats (Cd, 0.133 mM per liter for 2 months). The PALs were submitted to immunohistochemical and morphometric analysis to determine the percentage of lactotrophs (PRL-ir) and FSC (S-100-ir). Cultured PAL cells were stained with Hoechst 33258 to determine the presence of alterations in nuclear morphology consistent with apoptosis. The expressions of PLD and prolactin mRNA were assessed by RT-PCR. Cd treated rats showed a decrease of PLD mRNA levels that can be associated to both high number of apoptotic cells and increase of S-100 protein expression in FSC. Cd decreased prolactin mRNA expression, number of lactotrophs and percentage of PRL-ir suggesting a low availability of prolactin to be secreted from PAL. Cd modifies the lactotrophs activity of pituitary gland through biochemical, genomic and morphological changes and contributes directly or indirectly to the levels of serum prolactin.

Structural characteristics of the plasmid-encoded toxin from enteroaggregative Escherichia coli

Intoxication by the plasmid-encoded toxin (Pet) of enteroaggregative Escherichia coli requires toxin translocation from the endoplasmic reticulum (ER) to the cytosol. This event involves the quality control system of ER-associated degradation (ERAD), but the molecular details of the process are poorly characterized. For many structurally distinct AB-type toxins, ERAD-mediated translocation is triggered by the spontaneous unfolding of a thermally unstable A chain. Here we show that Pet, a non-AB toxin, engages ERAD by a different mechanism that does not involve thermal unfolding. Circular dichroism and fluorescence spectroscopy measurements demonstrated that Pet maintains most of its secondary and tertiary structural features at 37 degrees C, with significant thermal unfolding only occurring at temperatures >or=50 degrees C. Fluorescence quenching experiments detected the partial solvent exposure of Pet aromatic amino acid residues at 37 degrees C, and a cell-based assay suggested that these changes could activate an ERAD-related event known as the unfolded protein response. We also found that HEp-2 cells were resistant to Pet intoxication when incubated with glycerol, a protein stabilizer. Altogether, our data are consistent with a model in which ERAD activity is triggered by a subtle structural destabilization of Pet and the exposure of Pet hydrophobic residues at physiological temperature. This was further supported by computer modeling analysis, which identified a surface-exposed hydrophobic loop among other accessible nonpolar residues in Pet. From our data it appears that Pet can promote its ERAD-mediated translocation into the cytosol by a distinct mechanism involving partial exposure of hydrophobic residues rather than the substantial unfolding observed for certain AB toxins.

Evidence for the Regulatory Role of the N-terminal Helix of Secretory Phospholipase A2 from Studies on Native and Chimeric Proteins

The phospholipase A(2) (PLA(2)) enzymes are activated by binding to phospholipid membranes. Although the N-terminal alpha-helix of group I/II PLA(2)s plays an important role in the productive mode membrane binding of the enzymes, its role in the structural aspects of membrane-induced activation of PLA(2)s is not well understood. In order to elucidate membrane-induced conformational changes in the N-terminal helix and in the rest of the PLA(2), we have created semisynthetic human group IB PLA(2) in which the N-terminal decapeptide is joined with the (13)C-labeled fragment, as well as a chimeric protein containing the N-terminal decapeptide from human group IIA PLA(2) joined with a (13)C-labeled fragment of group IB PLA(2). Infrared spectral resolution of the unlabeled and (13)C-labeled segments suggests that the N-terminal helix of membrane-bound IB PLA(2) has a more rigid structure than the other helices. On the other hand, the overall structure of the chimeric PLA(2) is more rigid than that of the IB PLA(2), but the N-terminal helix is more flexible. A combination of homology modeling and polarized infrared spectroscopy provides the structure of membrane-bound chimeric PLA(2), which demonstrates remarkable similarity but also distinct differences compared with that of IB PLA(2). Correlation is delineated between structural and membrane binding properties of PLA(2)s and their N-terminal helices. Altogether, the data provide evidence that the N-terminal helix of group I/II PLA(2)s acts as a regulatory domain that mediates interfacial activation of these enzymes.

A novel calcium-sensitive switch revealed by the structure of human S100B in the calcium-bound form

BACKGROUND

S100B is a homodimeric member of the EF-hand calcium-binding protein superfamily. The protein has been implicated in cellular processes such as cell differentiation and growth, plays a role in cytoskeletal structure and function, and may have a role in neuropathological diseases, such as Alzheimers. The effects of S100B are mediated via its interaction with target proteins. While several studies have suggested that this interaction is propagated through a calcium-induced conformational change, leading to the exposure of a hydrophobic region of S100B, the molecular details behind this structural alteration remain unclear.

RESULTS

The solution structure of calcium-saturated human S100B (Ca(2+)-S100B) has been determined by heteronuclear NMR spectroscopy. Ca(2+)-S100B forms a well defined globular structure comprising four EF-hand calcium-binding sites and an extensive hydrophobic dimer interface. A comparison of Ca(2+)-S100B with apo S100B and Ca(2+)-calbindin D9k indicates that while calcium-binding to S100B results in little change in the site I EF-hand, it induces a backbone reorientation of the N terminus of the site II EF-hand. This reorientation leads to a dramatic change in the position of helix III relative to the other helices.

CONCLUSIONS

The calcium-induced reorientation of calcium-binding site II results in the increased exposure of several hydrophobic residues in helix IV and the linker region. While following the general mechanism of calcium modulatory proteins, whereby a hydrophobic target site is exposed, the 'calcium switch' observed in S100B appears to be unique from that of other EF-hand proteins and may provide insights into target specificity among calcium modulatory proteins.

Identification of cysteine ligands in metalloproteins using optical and NMR spectroscopy: cadmium-substituted rubredoxin as a model [Cd(CysS)4]2- center

Optical and NMR methods are presented for the identification of cysteine ligands in Cd-substituted metalloproteins, in particular those containing zinc-fingerlike motifs, using Cd-substituted Desulfovibrio gigas rubredoxin (Cd-Rd) as a model [Cd(CysS)4]2- complex. The 113Cd NMR spectrum of Cd-Rd contains a single 113Cd resonance with a chemical shift position (723.6 ppm) consistent with tetrathiolate metal coordination. The proton chemical shifts of the four cysteine ligands were obtained from one-dimensional heteronuclear (1H-113Cd) multiple quantum coherence (HMQC) and total coherence spectroscopy (TOCSY)-relayed HMQC experiments. In addition, sequential assignments were made for two short cysteine-containing stretches of the polypeptide chain using a combination of homonuclear proton correlated spectroscopy, TOCSY, and nuclear Overhauser effect spectroscopy experiments, enabling sequence-specific heteronuclear 3J(1H beta-113Cd) coupling constants for each cysteine to be determined. The magnitude of these couplings (0-38 Hz) follows a Karplus-like dependence with respect to the H beta-C beta-S gamma-Cd dihedral angles, inferred from the crystal structure of the native protein. The difference absorption envelope (Cd-Rd vs. apo-Rd) reveals three distinct transitions with Gaussian-resolved maxima located at 213, 229, and 245 nm, which are paralleled by dichroic features in the corresponding difference CD and magnetic CD spectra. Based on the optical electronegativity theory of Jørgensen, the lowest energy transition has been attributed to a CysS-Cd(II) charge-transfer excitation (epsilon 245, 26,000 M-1 cm-1) with a molar extinction coefficient per cysteine of 6,500 M-1 cm-1.(ABSTRACT TRUNCATED AT 250 WORDS)