The fact that aluminium (Al) and lead (Pb) are both toxic metals to living organisms, including human beings, was discovered a long time ago. Even when Al and Pb can reach and accumulate in almost every organ in the human body, the central nervous system is a particular target of the deleterious effects of both metals. Select human population can be at risk of Al neurotoxicity, and Al is proposed to be involved in the etiology of neurodegenerative diseases. Pb is a widespread environmental hazard, and the neurotoxic effects of Pb are a major public health concern. In spite of the numerous efforts and the accumulating evidence in this area of research, the mechanisms of Al and Pb neurotoxicity are still not completely elucidated. This review will particularly address the involvement of oxidative stress, membrane biophysics alterations, deregulation of cell signaling, and the impairment of neurotransmission as key aspects involved Al and Pb neurotoxicity.

Aluminium and lead: molecular mechanisms of brain toxicity

Principles Governing Mg, Ca, and Zn Binding and Selectivity in Proteins

1. Overview A 2. Protein Redesign B 2.1. Making Use of Native Proteins: Protein Redesign B 2.2. Protein Redesign Based on Functions C 2.2.1. Redesign of Zinc Finger Structural Sites C 2.2.2. Redesign of Zinc Hydrolytic Centers E 2.2.3. Redesign of Heme Centers J 2.2.4. Redesign of Nonheme Redox Centers M 2.2.5. Artificial Metalloenzymes for Regioand Enantioselective Catalysis AA 2.2.6. Redesigned Protein Assemblies as Nanoreactors AK 2.3. Summary AN 3. De Novo Design AN 3.1. A Minimalist Approach: Designing Proteins from Scratch AN 3.2. Interactions between De Novo Designed Peptides and Metal Ions AN 3.2.1. Heavy Metal Toxicity AO 3.2.2. De Novo Designed Metal Centers Based on β-Structures AT 3.2.3. Metal-Induced Protein Folding AV 3.3. De Novo Designed Functional Metalloproteins: The Grail Quest of Protein Design AX 3.3.1. De Novo Designed Hydrolytic Centers AX 3.3.2. De Novo Designed Electron Transfer Centers BB 3.3.3. Other Catalytic Centers BG 3.4. Summary BN 4. Perspective BO Author Information BO Corresponding Author BO Notes BO Biographies BO Abbreviations BR References BR

Protein design: toward functional metalloenzymes.

The biological chemistry of lead.

We present the synthesis, properties, and biological applications of Leadfluor-1 (LF1), a new water-soluble, turn-on fluorescent sensor that is capable of selectively imaging Pb2+ in aqueous solution and in living cells. LF1 combines a fluorescein chromophore and a pseudocrown receptor to provide good selectivity for Pb2+ over a range of biologically and environmentally relevant metal ions in aqueous solution, with sensitivity to parts per billion EPA limits for allowable lead in drinking water. In addition to these attributes, imaging experiments further show that LF1 is the first small-molecule reagent that can be delivered into living cells and report changes in intracellular Pb2+ levels.

A Selective Fluorescent Sensor for Detecting Lead in Living Cells

Recent studies suggest that the developmental toxicity associated with childhood lead poisoning may be attributable to interactions of Pb(II) with proteins containing thiol-rich structural zinc-binding sites. Here, we report detailed structural studies of Pb(II) in such sites, providing critical insights into the mechanism by which lead alters the activity of these proteins. X-ray absorption spectroscopy of Pb(II) bound to structural zinc-binding peptides reveals that Pb(II) binds in a three-coordinate Pb(II)-S3 mode, while Zn(II) is known to bind in a four-coordinate mode in these proteins. This Pb(II)-S_3 coordination in peptides is consistent with a trigonal pyramidal Pb(II)-S_3 model compound previously reported by Bridgewater and Parkin, but it differs from many other reports in the small molecule literature which have suggested Pb(II)-S_4 as a preferred coordination mode for lead. Reexamination of the published structures of these “Pb(II)-S_4” compounds reveals that, in almost all cases, the coordination number of Pb is actually 5, 6, or 8. The results reported herein combined with this new review of published structures suggest that lead prefers to avoid four-coordination in sulfur-rich sites, binding instead as trigonal pyramidal Pb(II)-S_3 or as Pb(II)-S_(5-8). In the case of structural zinc-binding protein sites, the observation that lead binds in a three-coordinate mode, and in a geometry that is fundamentally different from the natural coordination of zinc in these sites, explains why lead disrupts the structure of these peptides and thus provides the first detailed molecular understanding of the developmental toxicity of lead.

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Reexamination of lead(II) coordination preferences in sulfur-rich sites: implications for a critical mechanism of lead poisoning.

Here, we report that lead−thiolate charge-transfer bands (250−400 nm) can be used to monitor lead binding to cysteine-rich sites in proteins and report the application of this technique to determine the thermodynamics of lead binding to a series of structural zinc-binding domains. These studies reveal that Pb2+ binds tightly to structural zinc-binding domains with dissociation constants that range from KdPb = 10-9 to 10-14 M, depending on the number of cysteine residues in the metal-binding site. Competition experiments with Zn2+ lead to two striking conclusions:  first, the two metals rapidly equilibrate, and second, the ratio of Pb2+ to Zn2+ bound to a particular site is determined by the relative affinities of the two metals for that site, rather than being under kinetic control. We conclude that Pb2+ should be able to compete effectively with Zn2+ for Cys4 sites under physiological conditions. Despite the fact that Pb2+ binds tightly to cysteine-rich structural zinc sites, circular dichroism and 1H NM...

Lead Fingers: Pb2+ Binding to Structural Zinc-Binding Domains Determined Directly by Monitoring Lead−Thiolate Charge-Transfer Bands

Zinc binding to the two Cys(4) sites present in the DNA-binding domain (DBD) of nuclear hormone receptor proteins is required for proper folding of the domain and for protein activity. By utilizing Co(2+) as a spectroscopic probe, we have characterized the metal-binding properties of the two Cys(4) structural zinc-binding sites found in the DBD of human estrogen receptor alpha (hERalpha-DBD) and rat glucocorticoid receptor (GR-DBD). The binding affinity of Co(2+) to the two proteins was determined relative to the binding affinity of Co(2+) to the zinc finger consensus peptide, CP-1. Using the known dissociation constant of Co(2+) from CP-1, the dissociation constants of cobalt from hERalpha-DBD were calculated: K(d1)(Co) = 2.2 (+/- 1.0) x 10(-7) M and K(d2)(Co) = 6.1 (+/- 1.5) x 10(-7) M. Similarly, the dissociation constants of Co(2+) from GR-DBD were calculated: K(d1)(Co) = 4.1 (+/- 0.6) x 10(-7) M and K(d2)(Co) = 1.7 (+/- 0.3) x 10(-7) M. Metal-binding studies conducted in which Zn(2+) displaces Co(2+) from the metal-binding sites of hERalpha-DBD and GR-DBD indicate that Zn(2+) binds to each of the Cys(4) metal-binding sites approximately 3 orders of magnitude more tightly than Co(2+) does: the stoichiometric dissociation constants are K(d1)(Zn) = 1 (+/- 1) x 10(-10) M and K(d2)(Zn) = 5 (+/- 1) x 10(-10) M for hERalpha-DBD and K(d1)(Zn) = 2 (+/- 1) x 10(-10) M and K(d2)(Zn) = 3 (+/- 1) x 10(-10) M for GR-DBD. These affinities are comparable to those observed for most other naturally occurring structural zinc-binding sites. In contrast to the recent prediction by Low et. al. that zinc binding in these systems should be cooperative [Low, L. Y., Hernandez, H., Robinson, C. V., O'Brien, R., Grossmann, J. G., Ladbury, J. E., and Luisi, B. (2002) J. Mol. Biol. 319, 87-106], these data suggest that the zincs that bind to the two sites in the DBDs of hERalpha-DBD and GR-DBD do not interact.

John C. Payne

Papers

Reexamination of lead(II) coordination preferences in sulfur-rich sites: implications for a critical mechanism of lead poisoning.

Lead Fingers: Pb2+ Binding to Structural Zinc-Binding Domains Determined Directly by Monitoring Lead−Thiolate Charge-Transfer Bands

Spectroscopic determination of the binding affinity of Zinc to the DNA-binding domains of nuclear hormone receptors