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Although lead(II) is naturally not associated with nucleic acids, this metal ions has been applied with DNA and RNA in various contexts. Pb2+ is an excellent hydrolytic metal ion for nucleic acids, which is why it is mainly used as probing agent for secondary structure and to determine metal ion binding sites both in vitro and in vivo. A further application of lead(II) is in structural studies, i.e., NMR, but also in X-ray crystallography, mostly using this heavy metal to solve the phase problem in the latter method. The structures of tRNAPhe, RNase P, HIV-1 DIS, and the leadzyme are discussed here in detail. A major part of this review is devoted to the cleavage properties of lead(II) with RNA because of its excellence in catalyzing phosphodiester cleavage. Metal ion binding sites in large naturally occurring ribozymes are regularly determined by Pb2+ cleavage, and also in the in vitro selected socalled leadzyme, this metal ion is the decisive key to backbone cleavage at a specific site. Lead(II) was used in the first in vitro selection that yielded a catalytic DNA, i.e., the DNAzyme named GR5. Next to the GR5, the so-called 8-17E is the second most prominent DNAzyme today. Derivatives of these two lead(II)-dependent DNAzymes, as well as the G-quadruplex forming PS2.M have been applied to detect lead(II) in the lower nanomolar range not only in the test tube but also in body fluids. Due to the toxicity of lead(II) for living beings, this is a highly active research field. Finally, further applications of lead(II)-dependent DNAzymes, e.g., in the construction of nanocomputers, are also discussed.

Firstly, the self-stacking properties of ATP4- and the effects of metal ions and protons on these properties are described. Some examples involving macrochelate formation between phosphate-coordinated metal ions (M2+) and N7 of the adenine residue in MATP2- are discussed, and this is followed by considerations on mixed ligand complexes consisting of ATP4-, M2+, and amino acid anions with side chains that allow either aromatic-ring stacking or hydrophobic interactions with the adenine moiety; this gives rise to selectivity. Next, the properties of diphosphorylated 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA2-; Adefovir), i.e., of PMEApp4-, are compared with those of (2'-deoxy)ATP4- with regard to their metal ion-binding qualities, and in this way it can be explained why PMEApp2- is initially an excellent substrate for nucleic acid polymerases. Of course, after incorporation of the PMEA residue into the growing nucleic acid chain, this is terminated and this is how PMEA exerts its antiviral properties [its bis(pivaloyloxymethyl)ester, Adefovir dipivoxil, was recently approved for use in hepatitis B therapy]. Finally, the change in free energy connected with (macro)chelate formation or intramolecular stacking interactions and the effect of a reduced dielectric constant of the solvent on the stability of complexes and their structures in solution is considered

The macro acidity constants valid for aqueous solutions of several adenine, guanine,and hypoxanthine derivatives are summarized. It is shown how the application of the corresponding constants, e.g., for 7,9-dimethyladenine, allows a quantification of the intrinsic acidic properties of the (N1)H0/+ and (N7)H+ sites via micro acidity constants, and how to use this information for the calculation of the tautomeric ratios regarding the monoprotonated species, that is, N7-N1*H versus H*N7-N1, meaning that in one isomer H+ is at the N1 site and in the other at N7. It is further shown that different metal ions coordinated to a given site, e.g., N7, lead to a different extent of acidification, e.g., at (N1)H; the effect decreases in the series Cu2+>Ni2+>Pt2+ ~Pd2+. Moreover, the application of micro acidity constants proves that the acidifications are reciprocal and identical. This means, Pt2+ coordinated to (N1)-/0 sites in guanine, hypoxanthine, or adenine residues acidifies the (N7)H+ unit to the same extent as (N7)-coordinated Pt 2+ acidifies the (N1)H0/+ site. In other words, an apparently increased basicity of N7 upon Pt2+ coordination at (N1)-/0 sites disappears if the micro acidity constants of the appropriate isocharged tautomers of the ligand are properly taken into account. There is also evidence that proton-proton interactions are more pronounced than divalent metal ion-proton interactions, and that these in turn are possibly larger than divalent metal ion-metal ion interactions. The indicated quantifications of the acid-base properties are meaningful for nucleic acids including the formation of certain nucleobase tautomers in low concentrations, which could give rise to mutations

Cadmium(II), commonly classified as a relatively soft metal ion, prefers indeed aromatic-nitrogen sites (e.g., N7 of purines) over oxygen sites (like sugar-hydroxyl groups). However, matters are not that simple, though it is true that the affinity of Cd(2+) towards ribose-hydroxyl groups is very small; yet, a correct orientation brought about by a suitable primary binding site and a reduced solvent polarity, as it is expected to occur in a folded nucleic acid, may facilitate metal ion-hydroxyl group binding very effectively. Cd(2+) prefers the guanine(N7) over the adenine(N7), mainly because of the steric hindrance of the (C6)NH(2) group in the adenine residue. This Cd(2+)-(N7) interaction in a guanine moiety leads to a significant acidification of the (N1)H meaning that the deprotonation reaction occurs now in the physiological pH range. N3 of the cytosine residue, together with the neighboring (C2)O, is also a remarkable Cd(2+) binding site, though replacement of (C2)O by (C2)S enhances the affinity towards Cd(2+) dramatically, giving in addition rise to the deprotonation of the (C4)NH(2) group. The phosphodiester bridge is only a weak binding site but the affinity increases further from the mono- to the di- and the triphosphate. The same also holds for the corresponding nucleotides. Complex stability of the pyrimidine-nucleotides is solely determined by the coordination tendency of the phosphate group(s), whereas in the case of purine-nucleotides macrochelate formation takes place by the interaction of the phosphate-coordinated Cd(2+) with N7. The extents of the formation degrees of these chelates are summarized and the effect of a non-bridging sulfur atom in a thiophosphate group (versus a normal phosphate group) is considered. Mixed ligand complexes containing a nucleotide and a further mono- or bidentate ligand are covered and it is concluded that in these species N7 is released from the coordination sphere of Cd(2+). In the case that the other ligand contains

The review will discuss the influence of metal ions on conformational changes of oligonucleotides. First, a short definition of the torsion angles is given, followed by a concise yet critical overview of the commonly applied experimental techniques. Finally, the possible role of metals upon the following conformational changes of oligonucleotides is discussed: (i) the denaturation of double-strands, (ii) the transition from B- to A-DNA, (iii) the transition from right- to left-handed DNA and RNA, (iv) the condensation, (v) and other conformational changes. We conclude with a summary and outlook.

Metal ions are inextricably involved with nucleic acids due to their polyanionic nature. In order to understand the structure and function of RNAs and DNAs, one needs to have detailed pictures on the structural, thermodynamic, and kinetic properties of metal ion interactions with these biomacromolecules. In this review we first compile the physicochemical properties of metal ions found and used in combination with nucleic acids in solution. The main part then describes the various methods developed over the past decades to investigate metal ion binding by nucleic acids in solution. This includes for example hydrolytic and radical cleavage experiments, mutational approaches, as well as kinetic isotope effects. In addition, spectroscopic techniques like EPR, lanthanide(III) luminescence, IR and Raman as well as various NMR methods are summarized. Aside from gaining knowledge about the thermodynamic properties on the metal ion-nucleic acid interactions, especially NMR can be used to extract information on the kinetics of ligand exchange rates of the metal ions applied. The final section deals with the influence of anions, buffers, and the solvent permittivity on the binding equilibria between metal ions and nucleic acids. Little is known on some of these aspects, but it is clear that these three factors have a large influence on the interaction between metal ions and nucleic acids.

Metal ions are inextricably associated with RNAs of any size and control their folding and activity to a large part. In order to understand RNA mechanisms, also the positioning, affinities and kinetics of metal ion binding must be known. Due to the spectroscopic silence and relatively fast exchange rates of the metal ions usually associated with RNAs, this task is extremely challenging and thus numerous methods have been developed and applied in the past. Here we provide an overview on the different metal ions and methods applied in RNA (bio)chemistry: The physical-chemical properties of important metal ions are presented and briefly discussed with respect to their application together with RNA. Each method ranging from spectroscopic over biochemical to computational approaches is briefly described also mentioning caveats that might occur during the experiment and/or interpretation of the results

Since the discovery of catalytic RNA molecules (ribozymes), intense research has been devoted to understand their structure and activity. Among RNA molecules, the large ribozymes, namely group I and group II introns and RNase P, are of special importance. The first two ribozymes are known for their ability to perform self-splicing while RNase P is responsible for the 5'-end maturation of tRNA in bacteria, archea, and eukaryotes. All three groups of ribozymes show a significant requirement for metal ions in order to establish the active tertiary structure that enables catalysis. The primary role of both monovalent and divalent metal ions is to screen the negative charge associated with the phosphate sugar backbone, but the metal ions also play an active role in catalysis. Biochemical and biophysical investigations, supported by recent findings from X-ray crystal structures, allow clarifying and rationalizing both the structural and catalytic roles of metal ions in large ribozymes. In particular, the "two-metal-ion mechanism", describing how metal ions in the active center take part in catalysis, has been largely corroborated.

Certain heavy metals have been reported to seriously affect the immune system potentially resulting in a broad range of harmful health effects. Reported alterations in immune cell function include a variety of affected mechanisms. Thereby, depending on the particular metal, its concentration, route and duration of exposure, and biologic availability, the net outcome may be either immunosuppression or stimulation of immune cell activity. Since the key importance of the immune system is protection of the host against pathogenic agents, an impaired immune competence inevitably increases the susceptibility to invading pathogens. However, being aware that the immune system represents a sensitively regulated network of different cells, tissues, and soluble mediators it has to be stated that any form of dys-regulation may result in adverse health effects with overstimulation being as harmful as inhibition of functional activity. Chronic-inflammatory reactions, cancer development, hypersensitivity, allergic and autoimmune diseases are known consequences of persisting overstimulation. All these manifestations were already found to be related with heavy metal exposure.

Organisms in the environment experience exposure to mixtures of metals as a rule rather than an exception. Observational as well as experimental evidence shows that such co-exposure may give rise to combined effects that are different from what can be attributed to considering the effects of chemicals one by one. The two established reference models, concentration addition and response addition, therefore derive explicit expectations of a joint effect from the biological activities of the mixture constituents. The current empirical evidence of metal mixture effects in various mainly aquatic species shows, that while the reference models provide reasonable tools for analyzing combined effects, their actual predictions for binary mixtures compared to what has been observed show often somewhat less than additive combined effects. As the bioavailability of metals is governed by several environmental factors as well as biosystem properties, the different processes involved provide ample opportunities for interaction which may confound non-interactive combined effects. The biotic ligand model offers scope to address these issues on a more mechanism-focussed basis in the near future. Furthermore, the toxicodynamics of metals is highly compound-specific, considering the various specific metalloid transporters, regarding the essential functions of metals in metabolism and taking account of the organisms' efforts to maintain homeostasis for some metals. This and the diversity of already known molecular interferences with cellular metabolism offer scope to unravel potentially adverse interactive outcomes. Thus, for improving our predictability of combined effects from metal co-exposure, we require more quantitative insight into and models for the processes governing the toxicokinetics and dynamics of metals in environmental organisms.

The earliest perception restricted the occurrence of metallothioneins to animals, fungi, and certain bacteria and assigned the corresponding functions in plants to the enzymatically synthesized phytochelatins. This picture has now clearly changed, and the existence of plant metallothioneins is generally accepted. Compared to the vertebrate forms, plant metallothioneins show an intriguing sequence diversity, which is contrasted by an enormous lack of information about their possible functions, properties, and structures. The majority of functions proposed is derived from gene expression studies, which are reviewed with a not exhaustive but representative list of examples. However, it becomes evident that so far it is not possible to draw a clear-cut picture that ascribes specific functions to a given metallothionein. Rather, proposed functions overlap or are complementary to each other; sometimes even contradictory results are obtained. Regarding the structures and properties of the plant metallothionein proteins the amount of literature available is, compared to that of other MTs, considerably less comprehensive illustrating the early stages, in which this research area resides. Informations are at hand concerning the metal ion content of the different plant metallothionein species and metal-thiolate cluster stabilities, the number of clusters formed is proposed and predictions regarding the secondary structure are made. Three-dimensional data is so far restricted to one domain of a metallothionein from wheat providing fascinating insights into a cluster arrangement never reported for any metallothionein so far.

In 1957, Margoshes and Vallee reported on the isolation of a protein from horse kidney, which showed a high affinity for cadmium, and soon thereafter the protein was named metallothionein (MT) by the leading scientists Kägi and Vallee. Fifty years of intense research has dissected out many of the biochemical, molecular, and genetic aspects of these proteins, yet not that much is understood on its physiological putative functions. Being a highly conserved family of proteins would suggest essential biological functions, but these may be dispensable and/or assumed by other proteins as demonstrated by the phenotype of knock-out mice in normal conditions. Nevertheless, under challenging conditions (such as tissue injury) a strong phenotype appears that is suggestive of important physiological functions. This has been particularly well shown in the brain, where antiinflammatory, antioxidant and antiapoptotic effects of MT have been demonstrated. To date, the results gathered strongly support a therapeutic value of these proteins that deserve attention in clinical studies.

Metallothionein-3 (MT-3), also known as the neuronal growth inhibitory factor, has been discovered by Uchida and coworkers in 1991 in their search for a cellular component responsible for antagonizing aberrant neuritic sprouting and increased survival of cultured neurons stimulated by Alzheimer’s disease (AD) brain extract. Since this initial discovery further studies showed that MT-3 possesses peculiar structural and functional properties not shared by other members of the mammalian MT family. Several lines of evidence suggest that the metal-binding protein MT-3 plays a vital role in zinc and copper homeostasis in the brain. Although far from being understood, the unusual structural properties of MT-3 are responsible for its neuronal growth inhibitory activity, involvement in trafficking of zinc vesicles in the CNS, protection against copper-mediated toxicity in AD and in controlling abnormal metal-protein interactions in other neurodegenerative disorders.