Bibudhendra Sarkar

Metal coordination to carbohydrates. Structures and function

A. Introduction B. Overview (i) Synthetic carbohydrate chemistry (ii) Metal complexing carbohydrate derivatives (iii) Conformations of carbohydrates (iv) Role of the metal C. Specific examples (i) Alkali metals (ii) Alkaline earth metals including calcium (iii) Rare earth metals (iv) Molybdenum and vanadium (v) Chromium (vi) Manganese (vii) Iron (viii) Cobalt (ix) Nickel (x) Copper (xi) Zinc (xii) Lead (xiii) Others D. Applications (i) Biotechnology (ii) Agriculture (iii) Pharmaceutical E. Concluding remarks Acknowledgements References

Early treatment of Menkes disease with parenteral Cooper-Histidine: Long-term follow-up of four treated patients

We report on the long-term clinical course of 4 boys with Menkes disease, treated from early infancy with parenteral copper-histidine, with follow-up over 10-20 years. Three of the 4 had male relatives with a severe clinical course compatible with classical Menkes disease. As a consequence of early treatment, our patients have normal or near-normal intellectual development, but have developed many of the more severe somatic abnormalities of the related disorder, occipital horn syndrome, including severe orthostatic hypotension in 2. In addition, 1 boy developed a previously unreported anomaly, namely, massive splenomegaly and hypersplenism as a consequence of a splenic artery aneurysm. Previously reported molecular studies in 2 of these patients had shown gene defects which would have predicted a truncated and probably nonfunctional gene product. Despite the favorable effects on the neurological symptoms, parenteral copper treatment for Menkes disease should still be regarded as experimental. The development of more effective treatments must await a more precise delineation of the role which the Menkes protein plays in intracellular copper trafficking.

Reversible zinc exchange between metallothionein and the estrogen receptor zinc finger

We report here the first demonstration that reversible metal exchange occurs between metallothionein (MT) and full‐length estrogen receptor (ER). Specific binding of ER to estrogen response element is inhibited in the presence of 40 μM thionein and restored by 120 μM zinc. Moreover, ER in metal‐depleted nuclear extracts exhibits reduced DNA binding which can be restored by 140 μM native MT. Hence, thionein inhibits DNA binding by abstracting zinc from functional ER while native MT is capable of restoring binding to metal‐depleted extracts by donating metal to ER. This indicates MT may be an important physiological regulator of intracellular zinc and/or other metals.

Identification of Metal-binding Proteins in Human Hepatoma Lines by Immobilized Metal Affinity Chromatography and Mass Spectrometry

The metalloproteome is defined as the set of proteins that have metal-binding capacity by being metalloproteins or having metal-binding sites. A different metalloproteome may exist for each metal. Mass spectrometric characterization of metalloproteomes provides valuable information relating to cellular disposition of metals physiologically and in metal-associated diseases. We examined the Cu and Zn metalloproteomes in three human hepatoma lines: Hep G2 and Mz-Hep-1, which retain many functional characteristics of normal human hepatocytes, and SK-Hep-1, which is poorly differentiated. Additionally we studied a single specimen of normal human liver and Hep G2 cells depleted in vitro of cellular copper. We used matrix-assisted laser desorption ionization and electrospray ionization quadrupole time-of-flight mass spectrometry to analyze peptide sequences of tryptic digests obtained by either in-gel digestion of metal-binding proteins or peptides on an immobilized metal affinity chromatography column loaded with either Cu or Zn. Mainly high abundance proteins were identified. Cu-binding proteins identified included enolase, albumin, transferrin, and alcohol dehydrogenase as well as certain intracellular chaperone proteins. The Cu metalloproteome was not identical to the Zn metalloproteome. Peptide binding experiments demonstrated that Cu coordination prefers the order of residues histidine > methionine > cysteine. Although the Cu metalloproteome was similar from line to line, subtle differences were apparent. Gel profiling showed more extensive variation in expression of annexin II in SK-Hep-1 and Mz-Hep-1 than in Hep G2 and normal liver tissue. Glycerylphosphorylethanolamine was identified as a post-translational modification at residue Glu-301 of elongation factor 1-α in Hep G2. Intracellular copper depletion was associated with loss of the glycerylphosphoryl side group. These findings suggest that post-translational modification could be affected by intracellular actions of copper. Comparison of the Cu and Zn metalloproteomes in Hep G2 with a published general proteome of Hep G2 disclosed little overlap (Seow, T. K., et al. (2001) Proteomics 1, 1249–1263). Proteins in the metalloproteomes of human hepatocytes can be identified by these methods. Variations in these metalloproteomes may have important physiological relevance.

Public health strategies for western Bangladesh that address arsenic, manganese, uranium, and other toxic elements in drinking water.

Background More than 60,000,000 Bangladeshis are drinking water with unsafe concentrations of one or more elements. Objectives Our aims in this study were to evaluate and improve the drinking water testing and treatment plans for western Bangladesh. Methods We sampled groundwater from four neighborhoods in western Bangladesh to determine the distributions of arsenic, boron, barium, chromium, iron, manganese, molybdenum, nickel, lead, antimony, selenium, uranium, and zinc, and to determine pH. Results The percentages of tube wells that had concentrations exceeding World Health Organization (WHO) health-based drinking water guidelines were 78% for Mn, 48% for U, 33% for As, 1% for Pb, 1% for Ni, and 1% for Cr. Individual tube wells often had unsafe concentrations of both Mn and As or both Mn and U. They seldom had unsafe concentrations of both As and U. Conclusions These results suggest that the ongoing program of identifying safe drinking water supplies by testing every tube well for As only will not ensure safe concentrations of Mn, U, Pb, Ni, Cr, and possibly other elements. To maximize efficiency, drinking water testing in Bangladesh should be completed in three steps: 1) all tube wells must be sampled and tested for As; 2) if a sample meets the WHO guideline for As, then it should be retested for Mn and U; 3) if a sample meets the WHO guidelines for As, Mn, and U, then it should be retested for B, Ba, Cr, Mo, Ni, and Pb. All safe tube wells should be considered for use as public drinking water supplies.

Copper transport and its defect in Wilson disease: characterization of the copper-binding domain of Wilson disease ATPase

Copper is an essential trace element which forms an integral component of many enzymes. While trace amounts of copper are needed to sustain life, excess copper is extremely toxic. An attempt is made here to present the current understanding of the normal transport of copper in relation to the absorption, intracellular transport and toxicity. Wilson disease is a genetic disorder of copper transport resulting in the accumulation of copper in organs such as liver and brain which leads to progressive hepatic and neurological damage. The gene responsible for Wilson disease (ATP7B) is predicted to encode a putative copper-transporting P-type ATPase. An important feature of this ATPase is the presence of a large N-terminal domain that contains six repeats of a copper-binding motif which is thought to be responsible for binding this metal prior to its transport across the membrane. We have cloned, expressed and purified the N-terminal domain (approximately 70 kD) of Wilson disease ATPase. Metal-binding properties of the domain showed the protein to bind several metals besides copper; however, copper has a higher affinity for the domain. The copper is bound to the domain in Cu(I) form with a copper: protein ratio of 6.5:1. X-ray absorption studies strongly suggest Cu(I) atoms are ligated to cysteine residues. Circular dichroism spectral analyses suggest both secondary and tertiary structural changes upon copper binding to the domain. Copper-binding studies suggest some degree of cooperativity in binding of copper. These studies as well as detailed structural information of the copper-binding domain will be crucial in determining the specific role played by the copper-transporting ATPase in the homeostatic control of copper in the body and how the transport of copper is interrupted by mutations in the ATPase gene.

Bioinorganic Chemistry of Nickel

The toxicity caused by excessive intake of metals due to occupational or environmental pollution is a health problem throughout the world. In our programme of studying the biological transport of metals and its removal, a detailed investigation was carried out with Ni(II). The major Ni(II)-binding substances in human blood were found to be albumin and L-histidine. The Ni(II)-binding site of human albumin was shown to involve α-NH2 nitrogen, two intervening peptide nitrogens, imidazole nitrogen of the third histidine residue and the carboxyl side chain of the aspartic residue. Triethylenetetramine and D-penicillamine were found to be most efficient antidotal agents against Ni(II)-toxicity. A detailed Ni(II)-binding studies were undertaken with these chelating agents with a view to understand the reason for their efficiency in the removal of Ni(II).

Histatins: salivary peptides with copper(II)- and zinc(II)-binding motifs Perspectives for biomedical applications

Natural antimicrobial peptides represent a primordial mechanism of immunity in both vertebrate and nonvertebrate organisms. Among them, histatins belong to a family of human salivary metal‐binding peptides displaying potent antibacterial, antifungal and wound‐healing activities. These properties, along with the ability of histatins to inhibit collagenases and cysteine proteases, have attracted much attention for their potential use in the treatment of several oral diseases. This review critically assesses the studies carried out to date in order to provide a comprehensive and systematic vision of the information accumulated so far. In particular, the relationship between metal‐binding and peptide activity is extensively analysed. The review provides important clues for developing possible therapeutic applications of histatins and their synthetic peptide analogues by creating a set of necessary resource materials to support investigators and industries interested in exploiting their unique properties.

World Health Organization discontinues its drinking-water guideline for manganese.

Background: The World Health Organization (WHO) released the fourth edition of Guidelines for Drinking-Water Quality in July 2011. In this edition, the 400-µg/L drinking-water guideline for manganese (Mn) was discontinued with the assertion that because “this health-based value is well above concentrations of manganese normally found in drinking water, it is not considered necessary to derive a formal guideline value.” Objective: In this commentary, we review the WHO guideline for Mn in drinking water—from its introduction in 1958 through its discontinuation in 2011. Methods: For the primary references, we used the WHO publications that documented the Mn guidelines. We used peer-reviewed journal articles, government reports, published conference proceedings, and theses to identify countries with drinking water or potential drinking-water supplies exceeding 400 µg/L Mn and peer-reviewed journal articles to summarize the health effects of Mn. Discussion: Drinking water or potential drinking-water supplies with Mn concentrations > 400 µg/L are found in a substantial number of countries worldwide. The drinking water of many tens of millions of people has Mn concentrations > 400 µg/L. Recent research on the health effects of Mn suggests that the earlier WHO guideline of 400 µg/L may have been too high to adequately protect public health. Conclusions: The toxic effects and geographic distribution of Mn in drinking-water supplies justify a reevaluation by the WHO of its decision to discontinue its drinking-water guideline for Mn.

Direct Evidence of Nitrogen Coupling in the Copper(II) Complex of Bovine Serum Albumin by S-Band Electron Spin Resonance Technique

ESR spectra of the tight binding Cu(II) complex of bovine serum albumin (BSA) has been studied using S-band. At physiological pH, only one form of copper binding to BSA was detected from the ESR spectra. From previous X-band ESR spectra, nitrogen superhyperfine splittings were observable in the g perpendicular region; however, the resolution of the g parallel region was not sufficient to confirm the exact donor atoms of the complex. Using low-frequency ESR (2-4 GHz) at 77 K, we have resolved the nitrogen superhyperfine structure in the g parallel region. A computer simulation method has been developed for distinguishing between three and four nitrogen donor atoms. The Hyde-Froncisz theory of g and A strain broadening has been modified to use a field-swept calculation for the line shape. The observed intensity pattern and the computer simulation of such spectra positively confirm the structure of Cu(II) ion coordinated to four in-plane nitrogen atoms in frozen aqueous solutions of Cu(II)-BSA complexes at physiological pH. This is the first time that this binding site has been confirmed on the protein instead of a protein fragment or model compound. This work is another example of the usefulness of the S-band ESR technique for characterizing the metal-protein interactions when random variation in g factors cause line broadening in conventional X-band ESR spectra.