UNA MIRADA GLOBAL DEL ESTADO DE LAACUMULACIÓN POR METALES PESADOS POR HELMINTOS CON UNA NOTA EN EL USO DE CULTIVO IN VITRO DE ACANTOCÉFALOS ADULTOS PARA ESTUDIAR LOS MECANISMOS DE BIOACUMULACIÓN

Bioaccumulation of metals by helminths is a well acknowledged phenomenon that has triggered increasing research interest in the past two decades and found applications in environmental studies. The ecological literature is fairly abundant but still shows gaps with some taxa not having been studied. Variations in the ability of helminths to sequester various metals are recognized and a synthetic overview of the literature is provided herein. Adult acanthocephalans are known to be particularly efficient as bioaccumulators of heavy metals. We optimized an in vitro culture technique of the acanthocephalan Moniliformis moniliformis and initiated in vitro exposure to cadmium and lead. We propose to use this technique to study the mechanisms of uptake and sequestration of heavy metals, which are yet to be understood.La bioacumulación por metales por helmintos es un fenómeno bien reconocido que ha provocado un incremento de interés en investigación en las dos décadas pasadas y ha encontrado aplicaciones en estudios ambientales. La literatura ecológica es bastante abundante pero aun muestra lagunas con algunos taxas que no han sido estudiados. Variaciones en la habilidad de los helmintos para secuestrar varios metales son reconocidos y una sintética mirada global de la literatura es proporcionada aquí. Los acantocéfalos adultos son conocidos por ser particularmente eficientes como bioacumuladores de metales pesados. Optimizamos una técnica de cultivo in vitro del acantocéfalo Moniliformis moniliformise iniciamos una exposición in vitroa cadmio y plomo. Proponemos el uso de esta técnica para estudiar el mecanismo de captación y secuestro de metales, los cuales aun deben ser entendidos

Structural characterization of the manganese cluster of the oxygen evolving complex of photosystem II using x-ray absorption spectroscopy.

X-ray absorption spectroscopy (XAS) has been used to characterize the native (S\sb1) state and chemically altered forms of the tetranuclear Mn cluster responsible for photosynthetic water oxidation in the Oxygen Evolving Complex (OEC) of Photosystem II. EXAFS (Extended X-ray Absorption Fine Structure) has been used to characterize three interactions in the OEC: 1.86A Mn-O/N nearest neighbor interactions, 2.72A Mn\sp\...Mn vectors, and a 3.3A Mn\sp\...X interaction (X = C, Ca, or Mn). The identity of X was addressed by substituting Sr, Dy or La for the native Ca cofactor. Fitting trends indicate that the scatterer at 3.3A is most likely Mn with some contribution from carbon. XANES (X-ray Absorption Near Edge Structure) has been used to determine oxidation state of several chemically reduced species of the Mn cluster. The S\sb1 state exists in an oxidation state $>$(III)\sb4 and $$3A) Mn\sp\...Metal interactions is dependent on the distribution of ligands about the Mn. Destructive interference from an extremely disordered first shell of ligands can obscure the presence of both these structural features. There is a small but reproducible change in the 2.7A Mn\sp\...Mn distance when Ca\sp{2+} is replaced by Sr\sp{2+}, Dy\sp{3+} or La\sp{3+}. These changes are the first direct evidence for changes in the Mn\sb2(\mu-O)\sb2 core structure following Ca\sp{2+} replacement.Ph.D.ChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104535/1/9527729.pdfDescription of 9527729.pdf : Restricted to UM users only

Overviewof the status of heavy metal accumulation by helminths with a note on the use of in vitro culture of adult acanthocephalans to study the mechanisms of bioaccumulation

Bioaccumulation of metals by helminths is a well acknowledged phenomenon that has triggered increasing research interest in the past two decades and found applications in environmental studies. The ecological literature is fairly abundant but still shows gaps with some taxa not having been studied. Variations in the ability of helminths to sequester various metals are recognized and a synthetic overview of the literature is provided herein. Adult acanthocephalans are known to be particularly efficient as bioaccumulators of heavy metals. We optimized an in vitro culture technique of the acanthocephalan Moniliformis moniliformis and initiated in vitro exposure to cadmium and lead. We propose to use this technique to study the mechanisms of uptake and sequestration of heavy metals, which are yet to be understood.La bioacumulación por metales por helmintos es un fenómeno bien reconocido que ha provocado un incremento de interés en investigación en las dos décadas pasadas y ha encontrado aplicaciones en estudios ambientales. La literatura ecológica es bastante abundante pero aun muestra lagunas con algunos taxas que no han sido estudiados. Variaciones en la habilidad de los helmintos para secuestrar varios metales son reconocidos y una sintética mirada global de la literatura es proporcionada aquí. Los acantocéfalos adultos son conocidos por ser particularmente eficientes como bioacumuladores de metales pesados. Optimizamos una técnica de cultivo in vitro del acantocéfalo Moniliformis moniliformise iniciamos una exposición in vitroa cadmio y plomo. Proponemos el uso de esta técnica para estudiar el mecanismo de captación y secuestro de metales, los cuales aun deben ser entendidos

Interactions of Cu(I) with Selenium-Containing Amino Acids Determined by NMR, XAS, and DFT Studies

Cu(I) coordination by organoselenium compounds was recently reported as a mechanism for their prevention of copper-mediated DNA damage. To establish whether direct Se–Cu coordination may be involved in selenium antioxidant activity, Cu(I) coordination of the selenoamino acids methyl-<i>Se</i>-cysteine (MeSeCys) and selenomethionine (SeMet) was investigated. NMR results in D₂O indicate that Cu(I) binds to the Se atom of both MeSeCys and SeMet as well as the carboxylic acid oxygen atom(s) or amine nitrogen atoms. X-ray absorption spectroscopy (XAS) and density functional theory (DFT) results confirm Se–Cu coordination, with the identification of a 2.4 Å Se–Cu vector in both the Se- and Cu-EXAFS data. XAS studies also show Cu(I) in an unusual three-coordinate environment with the additional two ligands arising from O/N (2.0 Å). DFT models of 1:1 Cu-selenoamino acid complexes suggest that both selenoamino acids coordinate Cu(I) through the selenium and amino groups, with the third ligand assumed to be water. These compounds represent the first structurally characterized copper(I) complexes with sulfur- or selenium-containing amino acids

Specific Histidine Residues Confer Histatin Peptides with Copper-Dependent Activity against <i>Candida albicans</i>

The histidine-rich salivary peptides of the histatin family are known to bind copper (Cu) and other metal ions in vitro; however, the details of these interactions are poorly understood, and their implications for in vivo antifungal activity have not been established. Here, we show that the availability of Cu during exposure of <i>Candida albicans</i> to histatin-5 (Hist-5) modulates its antifungal activity. Antifungal susceptibility testing revealed that co-treatment of Hist-5 with Cu improved the EC₅₀ from ∼5 to ∼1 μM, whereas co-treatment with a high-affinity Cu-specific chelator abrogated antifungal activity. Spectrophotometric titrations revealed two previously unrecognized Cu­(I)-binding sites with apparent <i>K</i>_d values at pH 7.4, ∼20 nM, and confirmed a high-affinity Cu­(II)-binding site at the Hist-5 N-terminus with an apparent <i>K</i>_d of ∼8 pM. Evaluation of a series of His-to-Ala full-length and truncated Hist-5 peptides identified adjacent His residues (bis-His) as critical anchors for Cu(I) binding, with the presence of a third ligand revealed by X-ray absorption spectroscopy. On their own, the truncated peptides were ineffective at inhibiting the growth of <i>C. albicans</i>, but treatment with supplemental Cu resulted in EC₅₀ values down to ∼5 μM, approaching that of full-length Hist-5. The efficacy of the peptides depended on an intact bis-His site and correlated with Cu­(I) affinity. Together, these results establish new structure–function relationships linking specific histidine residues with Cu binding affinity and antifungal activity and provide further evidence of the involvement of metals in modulating the biological activity of these antifungal peptides

The Yeast Iron Regulatory Proteins Grx3/4 and Fra2 Form Heterodimeric Complexes Containing a [2Fe-2S] Cluster with Cysteinyl and Histidyl Ligation

The transcription of iron uptake and storage genes in S. cerevisiae is primarily regulated by the transcription factor Aft1. Nucleocytoplasmic shuttling of Aft1 is dependent upon mitochondrial Fe-S cluster biosynthesis via a signaling pathway that includes the cytosolic monothiol glutaredoxins (Grx3 and Grx4) and the BolA homologue Fra2. However the interactions between these proteins and the iron-dependent mechanism by which they control Aft1 localization are unclear. To reconstitute and characterize components of this signaling pathway in vitro, we have overexpressed yeast Fra2 and Grx3/4 in E. coli. We have shown that co-expression of recombinant Fra2 with Grx3 or Grx4 allows purification of a stable [2Fe-2S](2+) cluster-containing Fra2-Grx3 or Fra2-Grx4 heterodimeric complex. Reconstitution of a [2Fe-2S] cluster on Grx3 or Grx4 without Fra2 produces a [2Fe-2S]-bridged homodimer. UV-visible absorption and CD, resonance Raman, EPR, ENDOR, Mössbauer, and EXAFS studies of [2Fe-2S] Grx3/4 homodimers and the [2Fe-2S] Fra2-Grx3/4 heterodimers indicate that inclusion of Fra2 in the Grx3/4 Fe-S complex causes a change in the cluster stability and coordination environment. Taken together, our analytical, spectroscopic, and mutagenesis data indicate that Grx3/4 and Fra2 form a Fe-S-bridged heterodimeric complex with Fe ligands provided by the active site cysteine of Grx3/4, glutathione, and a histidine residue. Overall, these results suggest that the ability of the Fra2-Grx3/4 complex to assemble a [2Fe-2S] cluster may act as a signal to control the iron regulon in response to cellular iron status in yeast