The galvanization of biology: a growing appreciation for the roles of zinc

Analysis of zinc fingers optimized via phage display: evaluating the utility of a recognition code

Cys2His2 zinc finger proteins are composed of modular DNA-binding domains and provide an excellent framework for the design and selection of proteins with novel site specificity. Crystal structures of zinc finger-DNA complexes have shown that many Cys2His2 zinc fingers use a conserved docking arrangement that juxtaposes residues at key positions in the "recognition helix" with corresponding base positions in the three to four base-pair subsite. Several groups have proposed that specificity can be explained with a zinc finger-DNA recognition code that correlates specific amino acids at these key positions in the alpha-helix with specific bases in each position of the corresponding subsite. Here, we explore the utility of such a code through detailed studies of zinc finger variants selected via phage display. These proteins provide interesting systems for detailed analysis since they have affinities and specificities for their sites similar to those of naturally occurring DNA-binding proteins. Comparisons are facilitated by the fact that only key DNA-binding residues are varied in each finger while leaving all other regions of the structure unchanged. We study these proteins in detail by (1) selecting their optimal binding sites and comparing these binding sites with sites that might have been predicted from a code; (2) by examining the "evolutionary history" of these proteins during the phage display protocol to look for evidence of context-dependent effects; and (3) by reselecting finger 1 in the presence of the optimized finger 2/finger 3 domains to obtain further data on finger modularity. Our data for optimized fingers and binding sites demonstrate a clear correlation with contacts that would be predicted from a code. However, there are enough examples of context-dependent effects (not explained by any existing code) that selection is the most reliable method for maximizing the affinity and specificity of new zinc finger proteins.

Analysis of TFIIH subunit through isolation of the gene from Schizosaccharomyces pombe corresponding to that of Saccharomyces cerevisiae SSL1, reveals the presence of conserved structural motifs

We isolated a Schizosaccharomyces pombe (Sz. pombe) gene encoding the counterpart of the TFIIH subunit Homo sapiens (H. sapiens) p44 and Saccharomyces cerevisiae (S. cerevisiae) SSL1, and we named this gene product p47. Contrary to the case of SSL1, which is an essential gene of S. cerevisiae, p47 is not essential for the viability of Sz. pombe. The deduced amino acid sequence revealed that this TFIIH subunit is highly conserved during evolution. Comparison of the primary structures revealed differences in the predicted positions of introns in the Caenorhabditis elegans (C. elegans) gene encoding the p47 counterpart found during the genome project. A charged cluster in the N-terminal region is present in the two yeasts. Two putative zinc-binding motifs, an extended C2H2 zinc finger with a 'C8 motif' and a second putative zinc-binding motif common to the two TFIIH subunits, were also found, the former being completely conserved. The latter motif consists of five cysteine residues and is also present in hp44, SSL1 and another TFIIH subunit, human p34 (hp34). Since one zinc atom can bind to four ligands in zinc-binding motifs, the conservation of cysteine residues was given attention. This motif is completely conserved in p47 homologues derived from the four species. As one cysteine residue is not conserved among the homologues of hp34, the consensus of this motif is concluded to be Cys X2-Cys-X(10,12)-Cys-X2-Cys. This nucleotide sequence has been deposited in the GenBank Data Library under Accession Number AF017646.

Extended X-ray absorption fine structure evidence for a single metal binding domain in Xenopus laevis nucleotide excision repair protein XPA

Nucleotide excision repair (NER) is an important cellular mechanism, conserved from bacteria to humans, responsible for eliminating multiple types of structurally distinct DNA lesions from the genome. The protein XPA appears to play a central role in NER, recognizing and/or verifying damaged DNA and recruiting other proteins, including RPA, ERCC1, and TFIIH, to repair the damage. Sequence analysis and genetic evidence suggest that zinc, which is essential for DNA binding, is associated with a C4-type motif, C-X2-C-X17-C-X2-C. Sequence analysis suggests that a second, H2C2-type zinc-binding motif may be present near the C-terminal. Seventy percent of the amino acid sequence of Xenopus laevis XPA (xXPA) is identical to human XPA and both putative zinc-binding motifs are conserved in all known XPA proteins. Electrospray ionization-mass spectroscopy data show that xXPA contains only one zinc atom per molecule. EXAFS spectra collected on full-length xXPA in frozen (77 K) 15% glycerol aqueous solution unequivocally show that the zinc atom is coordinated to four sulfur atoms with an average Zn--S bond length of 2.33 +/- 0.02 A. Together, the EXAFS and mass spectroscopy data indicate that xXPA contains just one C4-type zinc-binding motif.

Microfine zinc oxide (Z-cote) as a photostable UVA/UVB sunblock agent

BACKGROUND

Microfine zinc oxide (Z-Cote) is used as a transparent broad-spectrum sunblock to attenuate UV radiation (UVR), including UVA I (340-400 nm).

OBJECTIVE

Our purpose was to assess the suitability of microfine zinc oxide as a broad-spectrum photoprotective agent by examining those properties generally considered important in sunscreens: attenuation spectrum, sun protection factor (SPF) contribution, photostability, and photoreactivity.

METHODS

Attenuation spectrum was assessed by means of standard spectrophotometric methods. SPF contribution was evaluated according to Food and Drug Administration standards. Photostability was measured in vitro by assessing SPF before and after various doses of UVR. Photoreactivity was evaluated by subjecting a microfine zinc oxide/organic sunscreen formulation to escalating doses of UVR and determining the percentage of organic sunscreen remaining.

RESULTS

Microfine zinc oxide attenuates throughout the UVR spectrum, including UVA I. It is photostable and does not react with organic sunscreens under irradiation.

CONCLUSION

Microfine zinc oxide is an effective and safe sunblock that provides broad-spectrum UV protection, including protection from long-wavelength UVA.

Binding properties of the artificial zinc fingers coding gene Sint1

On the basis of the recognition "code" that suggests specific rules between zinc finger's primary structure and the finger's potential DNA binding sites, we have constructed a new three-zinc finger coding gene to target the nine base pair DNA sequence: 5'-TGG-ATG-GAC-3'. This artificial gene named "Sint1" belongs to the Cys2-His2 zinc finger type. The amino acid positions, crucial for DNA binding, have been specifically chosen on the basis of the amino acid/base contacts more frequently represented in the available list of the proposed recognition "code". Here we demonstrate that Sint1 protein binds specifically the double strand "code" DNA target, with a dissociation constant (Kd) comparable to the Kd of the well known Zif268 protein. Sint1 "code" deduced and the "experimental" selected DNA binding sites share five nucleotide positions. Interestingly, Sint1 shows both high affinity and specificity toward the single strand "code" DNA binding site, with a Kd comparable to the corresponding double strand DNA target. Moreover, we prove that Sint1 is able to bind RNA similarly to several natural zinc finger proteins.

Zinc fingers in Caenorhabditis elegans: finding families and probing pathways

More than 3 percent of the protein sequences inferred from the Caenorhabditis elegans genome contain sequence motifs characteristic of zinc-binding structural domains, and of these more than half are believed to be sequence-specific DNA-binding proteins. The distribution of these zinc-binding domains among the genomes of various organisms offers insights into the role of zinc-binding proteins in evolution. In addition, the complete genome sequence of C. elegans provides an opportunity to analyze, and perhaps predict, pathways of transcriptional regulation.

Novel insights into structure and function of MRP8 (S100A8) and MRP14 (S100A9)

The two migration inhibitory factor- (MIF)-related protein-8 (MRP8; S100A8) and MRP14 (S100A9) are two calcium-binding proteins of the S100 family. These proteins are expressed during myeloid differentiation, are abundant in granulocytes and monocytes, and form a heterodimeric complex in a Ca2+-dependent manner. Phagocytes expressing MRP8 and MRP14 belong to the early infiltrating cells and dominate acute inflammatory lesions. In addition, elevated serum levels of MRP8 and MRP14 have been found in patients suffering from a number of inflammatory disorders including cystic fibrosis, rheumatoid arthritis, and chronic bronchitis, suggesting conceivable extracellular roles for these proteins. Although a number of possible functions for MRP8/14 have been proposed, the biological function still remains unclear. This review addresses recent developments regarding the MRP14-mediated promotion of leukocyte-endothelial cell-interactions and the characterization of MRP8/14 heterodimers as a fatty acid binding protein complex. In view of the current knowledge, the authors will hypothesize that MRP8 and MRP14 play an important role in leukocyte trafficking, but do not affect neutrophil effector functions.

AtMSI4 and RbAp48 WD-40 repeat proteins bind metal ions

The mammalian RbAp48 protein is the most extensively studied member of the conserved family of Msi1-like WD-40 repeat proteins, which are components of complexes involved in the assembly and modification of chromatin. We have isolated a plant homolog of RbAp48, AtMSI4. By metal affinity chromatography, zinc blotting and atomic absorption analysis, we demonstrate that purified recombinant RbAp48 and AtMSI4 proteins bind 3-4 metal ions per molecule of protein. Metal competition assays indicate a preference for zinc. Both N- and C-terminal halves of RbAp48 and AtMSI4 display zinc binding activity, suggesting it is an intrinsic property of the propeller structures likely to be formed by these proteins. Metal binding might mediate and/or regulate protein-protein interactions which are functionally important in chromatin metabolism.

Ichthyophthirius multifiliis: a model of cutaneous infection and immunity in fishes

The parasitic ciliate Ichthyophthirius multifiliis offers a useful system for the study of cutaneous immunity against an infectious microorganism. Naive fish usually die following infection, but animals surviving sublethal parasite exposure become resistant to subsequent challenge. This resistance correlates with the presence of humoral antibodies in the sera and cutaneous mucus of immune fish. A mechanism of immunity has recently been elucidated that involves antibody binding to surface proteins (referred to as immobilization antigens or i-antigens) located on the parasite cell and ciliary membranes. Antibody-mediated cross-linking of i-antigens triggers a response by the parasite resulting in its exit from the host. These effects can be observed directly on the surface of live fish. In addition to allowing the observation of effector responses in vivo, Ichthyophthirius also provides a means to study the ontogeny of the mucosal immune response. The sites of antigen capture and presentation, and the sites of antibody production, are unknown with regard to cutaneous immunity. Because the external epithelial surfaces of fish are often the points of pathogen entry, a basic understanding of the inductive immune mechanisms and immune cell interactions in the skin and gills is extremely important with regard to vaccine development. The development of Ichthyophthirius as an experimental system and how it might be used to address these issues are discussed in this review.

Retinal targets for calmodulin include proteins implicated in synaptic transmission

Ca2+ influxes regulate multiple events in photoreceptor cells including phototransduction and synaptic transmission. An important Ca2+ sensor in Drosophila vision appears to be calmodulin since a reduction in levels of retinal calmodulin causes defects in adaptation and termination of the photoresponse. These functions of calmodulin appear to be mediated, at least in part, by four previously identified calmodulin-binding proteins: the TRP and TRPL ion channels, NINAC and INAD. To identify additional calmodulin-binding proteins that may function in phototransduction and/or synaptic transmission, we conducted a screen for retinal calmodulin-binding proteins. We found eight additional calmodulin-binding proteins that were expressed in the Drosophila retina. These included six targets that were related to proteins implicated in synaptic transmission. Among these six were a homolog of the diacylglycerol-binding protein, UNC13, and a protein, CRAG, related to Rab3 GTPase exchange proteins. Two other calmodulin-binding proteins included Pollux, a protein with similarity to a portion of a yeast Rab GTPase activating protein, and Calossin, an enormous protein of unknown function conserved throughout animal phylogeny. Thus, it appears that calmodulin functions as a Ca2+ sensor for a broad diversity of retinal proteins, some of which are implicated in synaptic transmission.

HIV-1 gag proteins: diverse functions in the virus life cycle

The Gag proteins of HIV-1, like those of other retroviruses, are necessary and sufficient for the assembly of virus-like particles. The roles played by HIV-1 Gag proteins during the life cycle are numerous and complex, involving not only assembly but also virion maturation after particle release and early postentry steps in virus replication. As the individual Gag domains carry out their diverse functions, they must engage in interactions with themselves, other Gag proteins, other viral proteins, lipid, nucleic acid (DNA and RNA), and host cell proteins. This review briefly summarizes our current understanding of how HIV-1 Gag proteins function in the virus life cycle.

Zinc-binding of endostatin is essential for its antiangiogenic activity

Endostatin is a potent angiogenesis inhibitor in vitro and in vivo. We used the yeast Pichia pastoris to express and purify soluble endostatin. It was discovered that metal chelating agents can induce N-terminal degradation of endostatin. We theorized that a metal was removed from endostatin which changed the conformation and allowed a contaminating protease to degrade the N-terminus. Atomic absorption and amino acid analysis of endostatin purified from Pichia pastoris and mammalian cells showed a 1:1 molar ratio of Zn2+ to protein. Ding et al. have shown that histidines 1, 3, 11, and aspartic acid 76 coordinate the Zn2+ atom (1). An H1/3A double, an H11A, and a D76A single mutant of endostatin were not able to regress Lewis lung carcinoma. We conclude that the ability of endostatin to bind Zn2+ is essential for its antiangiogenic activity.

Role of the putative zinc finger domain of Saccharomyces cerevisiae DNA polymerase epsilon in DNA replication and the S/M checkpoint pathway

It has been proposed that C-terminal motifs of the catalytic subunit of budding yeast polymerase (pol) epsilon (POL2) couple DNA replication to the S/M checkpoint (Navas, T. A., Zheng, Z., and Elledge, S. J. (1995) Cell 80, 29-39). Scanning deletion analysis of the C terminus reveals that 20 amino acid residues between two putative C-terminal zinc fingers are essential for DNA replication and for an intact S/M cell cycle checkpoint. All mutations affecting the inter-zinc finger amino acids or the zinc fingers themselves are sensitive to methylmethane sulfonate and have reduced ability to induce RNR3, showing that the mutants are defective in the transcriptional response to DNA damage as well as the cell cycle response. The mutations affect the assembly of the pol epsilon holoenzyme. Two-hybrid assays show that the POL2 subunit interacts with itself, and that the replication and checkpoint mutants are specifically defective in the interaction, suggesting (but not proving) that direct or indirect dimerization may be important for the normal functions of pol epsilon. The POL2 C terminus is sufficient for interaction with DPB2, the essential and phylogenetically conserved subunit of pol epsilon, but not for interaction with DPB3. Neither Dpb3p nor Dpb2p homodimerizes in the two-hybrid assay.

Functional analysis of ZNF85 KRAB zinc finger protein, a member of the highly homologous ZNF91 family

We previously identified the ZNF85 (HPF4) KRAB zinc finger gene, a member of the human ZNF91 family. Here, we show that the ZNF85 gene is highly expressed in normal adult testis, in seminomas, and in the NT2/D1 teratocarcinoma cell line. Immunocytochemical localization of a panel of beta-Gal/ZNF85 fusion proteins revealed that ZNF85 contains at least one nuclear localization signal located in the spacer region connecting the KRAB domain with the zinc finger repeats. Bacterially expressed ZNF85 zinc finger domain bound strongly and exclusively to DNA in vitro in a zinc-dependent manner. The KRAB(A) domain of the ZNF85 protein and of several other members of the ZNF91 family exhibited repressing activity when tested in Gal4 fusion protein assays. The repression was significantly enhanced by the addition of the KRAB (B) domain, whereas further addition of other conserved regions had no effect. The ZNF85 KRAB(A) and (B) domains in vitro bound several nuclear proteins that might constitute critical cofactors for repression.

The Zn(II) binding motifs of E. coli DNA topoisomerase I is part of a high-affinity DNA binding domain

Escherichia coli DNA topoisomerase I binds three Zn(II) with three tetracysteine motifs. Three subclones containing these tetracysteine motifs were expressed and purified. Subclone ZD1 contained the minimal tetracysteine motifs sequence. A larger subclone ZD2 corresponded to a region bordered by two protease sensitive sites. Subclone ZD3 also included the 14-kDa C-terminal domain that has been shown to bind DNA. Subclones ZD1 and ZD2 were found to bind one and two Zn(II), respectively, and neither had detectable DNA binding activity. ZD3 could bind three Zn(II) and had higher DNA binding affinity than the 14-kDa C-terminal domain. The complex formed between ZD3 and a single-stranded 31mer could be detected by the gel shift assay while the complex formed by the 14-kDa C-terminal domain was not stable under gel electrophoresis conditions. The three Zn(II) binding motifs appeared to be part of a high-affinity DNA binding domain.

Widespread occurrence of a highly conserved RING-H2 zinc finger motif in the model plant Arabidopsis thaliana

Several novel Arabidopsis thaliana proteins containing a RING-H2 zinc finger motif were predicted after database searches. Alignment of 29 RING-H2 finger sequences shows that the motif is strikingly conserved in otherwise unrelated proteins. Only short, non-conserved polar/charged sequences distinguish these domains. The RING-H2 domain is most often present in multi-domain structures, a number of which are likely to contain a membrane-spanning region or an additional zinc finger. However, there are several small (126-200 residues) proteins consisting of an N-terminal domain, rich in aliphatic residues, and a C-terminal RING-H2 domain. Reverse-transcription PCR suggests that the RING-H2 genes are widely expressed at low levels.

Functional dissection of Arabidopsis COP1 reveals specific roles of its three structural modules in light control of seedling development

Arabidopsis COP1 acts as a repressor of photomorphogenesis in darkness, and light stimuli abrogate the repressive ability and nuclear abundance of COP1. COP1 has three known structural modules: an N-terminal RING-finger, followed by a predicted coiled-coil and C-terminal WD-40 repeats. A systematic study was undertaken to dissect the functional roles of these three COP1 domains in light control of Arabidopsis seedling development. Our data suggest that COP1 acts primarily as a homodimer, and probably dimerizes through the coiled-coil domain. The RING-finger and the coiled-coil domains can function independently as light-responsive modules mediating the light-controlled nucleocytoplasmic partitioning of COP1. The C-terminal WD-40 domain functions as an autonomous repressor module since the overexpression of COP1 mutant proteins with intact WD-40 repeats are able to suppress photomorphogenic development. This WD-40 domain-mediated repression can be at least in part accounted for by COP1's direct interaction with and negative regulation of HY5, a bZIP transcription factor that positively regulates photomorphogenesis. However, COP1 self-association is a prerequisite for the observed interaction of the COP1 WD-40 repeats with HY5. This work thus provides a structural basis of COP1 as a molecular switch.

Inactivation of human immunodeficiency virus type 1 infectivity with preservation of conformational and functional integrity of virion surface proteins

Whole inactivated viral particles have been successfully used as vaccines for some viruses, but procedures historically used for inactivation can denature virion proteins. Results have been inconsistent, with enhancement of disease rather than protection seen in some notable instances following vaccination. We used the compound 2,2'-dithiodipyridine (aldrithiol-2; AT-2) to covalently modify the essential zinc fingers in the nucleocapsid (NC) protein of human immunodeficiency virus type 1 (HIV-1) or simian immunodeficiency virus (SIV) virions, thereby inactivating infectivity. The inactivated virus was not detectably infectious in vitro (up to 5 log units of inactivation). However, in contrast to virions inactivated by conventional methods such as heat or formalin treatment, viral and host cell-derived proteins on virion surfaces retained conformational and functional integrity. Thus, immunoprecipitation of AT-2-treated virions was comparable to precipitation of matched untreated virus, even when using antibodies to conformational determinants on gp120. AT-2 inactivated virions bound to CD4(+) target cells and mediated virus-induced, CD4-dependent "fusion from without" comparably to native virions. However, viral entry assays demonstrated that the viral life cycle of AT-2-treated virions was arrested before initiation of reverse transcription. The major histocompatibility complex (MHC) class II molecules on the surface of AT-2-treated virions produced from MHC class II-expressing cells retained the ability to support class II-dependent, superantigen-triggered proliferative responses by resting T lymphocytes. These findings indicate that inactivation via this method results in elimination of infectivity with preservation of conformational and functional integrity of virion surface proteins, including both virally encoded determinants and proteins derived from the host cells in which the virus was produced. Such inactivated virions should provide a promising candidate vaccine antigen and a useful reagent for experimentally probing the postulated involvement of virion surface proteins in indirect mechanisms of HIV-1 pathogenesis.

Comparing genomes in terms of protein structure: surveys of a finite parts list

We give an overview of the emerging field of structural genomics, describing how genomes can be compared in terms of protein structure. As the number of genes in a genome and the total number of protein folds are both quite limited, these comparisons take the form of surveys of a finite parts list, similar in respects to demographic censuses. Fold surveys have many similarities with other whole-genome characterizations, e.g., analyses of motifs or pathways. However, structure has a number of aspects that make it particularly suitable for comparing genomes, namely the way it allows for the precise definition of a basic protein module and the fact that it has a better defined relationship to sequence similarity than does protein function. An essential requirement for a structure survey is a library of folds, which groups the known structures into 'fold families.' This library can be built up automatically using a structure comparison program, and we described how important objective statistical measures are for assessing similarities within the library and between the library and genome sequences. After building the library, one can use it to count the number of folds in genomes, expressing the results in the form of Venn diagrams and 'top-10' statistics for shared and common folds. Depending on the counting methodology employed, these statistics can reflect different aspects of the genome, such as the amount of internal duplication or gene expression. Previous analyses have shown that the common folds shared between very different microorganisms, i.e., in different kingdoms, have a remarkably similar structure, being comprised of repeated strand-helix-strand super-secondary structure units. A major difficulty with this sort of 'fold-counting' is that only a small subset of the structures in a complete genome are currently known and this subset is prone to sampling bias. One way of overcoming biases is through structure prediction, which can be applied uniformly and comprehensively to a whole genome. Various investigators have, in fact, already applied many of the existing techniques for predicting secondary structure and transmembrane (TM) helices to the recently sequenced genomes. The results have been consistent: microbial genomes have similar fractions of strands and helices even though they have significantly different amino acid composition. The fraction of membrane proteins with a given number of TM helices falls off rapidly with more TM elements, approximately according to a Zipf law. This latter finding indicates that there is no preference for the highly studied 7-TM proteins in microbial genomes. Continuously updated tables and further information pertinent to this review are available over the web at http://bioinfo.mbb.yale.edu/genome.

HRT, a novel zinc finger, transcriptional repressor from barley

A barley gene encoding a novel DNA-binding protein (HRT) was identified by southwestern screening with baits containing a gibberellin phytohormone response element from an alpha-amylase promoter. The HRT gene contains two introns, the larger of which (5722 base pairs (bp)) contains a 3094-bp LINE-like element with homology to maize Colonist1. In vitro mutagenesis and zinc- and DNA-binding assays demonstrate that HRT contains three unusual zinc fingers with a CX8-9CX10CX2H consensus sequence. HRT is targeted to nuclei, and homologues are expressed in other plants. In vivo, functional tests in plant cells indicate that full-length HRT can repress expression from certain promoters including the Amy1/6-4 and Amy2/32 alpha-amylase promoters. In contrast, truncated forms of HRT containing DNA-binding domains can activate, or derepress, transcription from these promoters. Northern hybridizations indicate that HRT mRNA accumulates to low levels in various tissues. Roles for HRT in mediating developmental and phytohormone-responsive gene expression are discussed.

Coordination of Zn2+ (and Cd2+) by prokaryotic metallothionein. Involvement of his-imidazole

In mammalian metallothionein Zn2+ is exclusively coordinated to Cys-thiolate to form clusters in which the metal is thermodynamically stable but also kinetically labile. By contrast, little is known about coordination to prokaryotic metallothionein, SmtA. 3 nmol of Zn2+ nmol-1 SmtA were displaced by 8 nmol of p-(hydroxymercuri)phenylsulfonate implicating eight of the nine Cys in the coordination of three metal ions. None of the Zn2+ associated with SmtA was accessible to 4-(2-pyridylazo)resorcinol prior to the addition of p-(hydroxymercuri)phenylsulfonate. An unusual feature of SmtA is the presence of three His residues, and we have investigated whether these contribute to metal coordination. Less Zn2+ was associated with purified SmtA(H40R/H49R/H55R), in which all three His residues were substituted with Arg, and approximately one equivalent of Zn2+ was immediately accessible to 4-(2-pyridylazo)resorcinol. Following incubation of SmtA with 111Cd, three 111Cd resonances were detected, two in a range expected for CdS4 and the third indicative of either CdNS3 or CdN2S2 coordination. Two-dimensional TOCSY 1H NMR and 111Cd-edited 1H NMR showed two His residues bound to 111Cd, confirming CdN2S2 coordination. The pH of half-dissociation of Zn2+ increased from 4.05 for SmtA to 5.37 for SmtA(H40R/H49R/H55R). Equivalent values for single His mutants SmtA(H40R), SmtA(H49R), and SmtA(H55R) were 4.62, 4.48, and 3.81, respectively, revealing that conversion of His40 or His49 to Arg impairs Zn2+ binding at the CdN2S2 and CdS4 sites. Only approximately two equivalents of Zn2+ were associated with purified SmtA(H49R). The appearance of a fourth 111Cd resonance at lower pH suggests that an alternative CdN2S2 site also exists.

Effect of redox conditions on the DNA-binding efficiency of the retinoic acid receptor zinc-finger

Retinoic acid and its derivatives are involved in many important biological processes. In the present study, we have shown that the DNA binding domain of the retinoic acid receptor, which contains two zinc fingers with the Zn(II) tetrahedrally coordinated by four Cys, is susceptible to intracellularly relevant oxidizing agents. In the presence of hydrogen peroxide or hypochlorite, the zinc-finger DNA binding activity was abolished in a concentration dependent manner. The loss of DNA binding activity was correlated with the release of Zn(II) from the zinc-finger motif as a consequence of Zn(II)-thiolate bond oxidation. A combination of glutathione and Zn(II) was able to restore the activity, suggesting that oxidation of the zinc-finger by hydrogen peroxide or hypochlorite resulted in the formation of disulfide bonds between the Cys present in the Zn(II)-binding motif. Our results indicate that in situations of oxidative-stress zinc-finger containing transcription factors may be particularly susceptible to oxidation, resulting in the disruption of control and regulation of gene expression.

Human nucleotide excision repair protein XPA: extended X-ray absorption fine-structure evidence for a metal-binding domain

The ubiquitous, multi-enzyme, nucleotide excision repair (NER) pathway is responsible for correcting a wide range of chemically and structurally distinct DNA lesions in the eukaryotic genome. Human XPA, a 31 kDa, zinc-associated protein, is thought to play a major NER role in the recognition of damaged DNA and the recruitment of other proteins, including RPA, ERCC1, and TFIIH, to repair the damage. Sequence analyses and genetic evidence suggest that zinc is associated with a C4-type motif, C105-X2-C108-X17-C126-X2-C129, located in the minimal DNA binding region of XPA (M98-F219). The zinc-associated motif is essential for damaged DNA recognition. Extended X-ray absorption fine structure (EXAFS) spectra collected on the zinc associated minimal DNA-binding domain of XPA (ZnXPA-MBD) show directly, for the first time, that the zinc is coordinated to the sulfur atoms of four cysteine residues with an average Zn-S bond length of 2.34+/-0.01 A. XPA-MBD was also expressed in minimal medium supplemented with cobalt nitrate to yield a blue-colored protein that was primarily (>95%) cobalt associated (CoXPA-MBD). EXAFS spectra collected on CoXPA-MBD show that the cobalt is also coordinated to the sulfur atoms of four cysteine residues with an average Co-S bond length of 2.33+/-0.02 A.

Personal reflections on a galvanizing trail

This article encompasses my perception of, and experience in, an exciting segment of the trace element era in nutrition research: the role of zinc in the nutrition of animals and humans. Zinc has been a major player on the stage of trace element research, and it has left a trail that galvanized the attention of many researchers, including myself. It is ubiquitous in biological systems, and it plays a multitude of physiologic and biochemical functions. A brief historical overview is followed by a discussion of the contributions the work done in my laboratory has made toward understanding the physiological and biochemical functions of zinc. The effort of 40 years has led to the belief that one of zinc's major roles, and perhaps its first limiting role, is to preserve plasma-membrane function as regards ion channels and signal transduction. Although substantial knowledge has been gained relating to the importance of zinc in nutrition, much remains to be discovered.

Effects of Zn2+ on wild and mutant neuronal alpha7 nicotinic receptors

Zn2+ is a key structural/functional component of many proteins and is present at high concentrations in the brain and retina, where it modulates ligand-gated receptors. Therefore, a study was made of the effects of zinc on homomeric neuronal nicotinic receptors expressed in Xenopus oocytes after injection of cDNAs encoding the chicken wild or mutant alpha7 subunits. In oocytes expressing wild-type receptors, Zn2+ alone did not elicit appreciable membrane currents. Acetylcholine (AcCho) elicited large currents (IAcCho) that were reduced by Zn2+ in a reversible and dose-dependent manner, with an IC50 of 27 microM and a Hill coefficient of 0.4. The inhibition of IAcCho by Zn2+ was competitive and voltage-independent, a behavior incompatible with a channel blockade mechanism. In sharp contrast, in oocytes expressing a receptor mutant, with a threonine-for-leucine 247 substitution (L247Talpha7), subnanomolar concentrations of Zn2+ elicited membrane currents (IZn) that were reversibly inhibited by the nicotinic receptor blockers methyllycaconitine and alpha-bungarotoxin. Cell-attached single-channel recordings showed that Zn2+ opened channels that had a mean open time of 5 ms and a conductance of 48 pS. At millimolar concentrations Zn2+ reduced IAcCho and the block became stronger with cell hyperpolarization. Thus, Zn2+ is a reversible blocker of wild-type alpha7 receptors, but becomes an agonist, as well as an antagonist, following mutation of the highly conserved leucine residue 247 located in the M2 channel domain. We conclude that Zn2+ is a modulator as well as an activator of homomeric nicotinic alpha7 receptors.

A carboxyl-terminal Cys2/His2-type zinc-finger motif in DNA primase influences DNA content in Synechococcus PCC 7942

The DNA primase gene, dnaG, has been isolated from the cyanobacterium Synechococcus PCC 7942. It is not part of a macromolecular synthesis operon but is co-transcribed with pheT and located adjacent to the metallothionein divergon, smt. At the carboxyl terminus of this DnaG is a Cys2/His2 zinc-finger motif. The carboxyl-terminal 91 residues bound 65Zn and 0.95 g atom of Zn2+ mol-1 were detected with 4-(2-pyridylazo)resorcinol. Following exposure to Cd2+, 0.95 g atom of Cd2+ was displaced by 2 equivalents of p-(hydroxymercuri) phenylsulfonate mol-1, while only 0.03 g atom of Cd2+ was displaced mol-1 polypeptide missing the carboxyl-terminal (residue 592 onward) zinc-finger motif. Zn2+ caused an increase in intensity, and a reduction in wavelength, of Trp fluorescence at the tip of the predicted zinc-finger, while EDTA caused the converse. Cells containing a single chromosomal codon substitution (C597S), altering the zinc-finger, were generated by exploiting Zn2+-sensitive smt mutants and the proximity of dnaG to smt. Cells in which smt and dnaG(C597S) had integrated into the chromosome were selected via restored Zn2+ tolerance. Synechococcus PCC 7942 and its dnaG(C597S) mutant grew at equivalent rates, but the latter had a reduced number of chromosomes.

Zinc Bound to the Killer Cell-Inhibitory Receptor Modulates the Negative Signal in Human NK Cells

The lysis of target cells by human NK cells is inhibited by several kinds of receptors with varying specificities for the MHC class I molecules of target cells. The requirements for complete inhibition of NK cytotoxicity appear to be complex and not well defined. The HLA-C-specific members of the killer cell-inhibitory receptor (KIR) family, carrying two Ig domains (KIR2D), are unusual among Ig superfamily members in their ability to bind zinc. A role for the zinc-binding site in KIR-mediated inhibition was demonstrated in this study using a functional reconstitution system in NK cells. Replacement of six histidines by alanine residues in putative zinc binding sites of a KIR2D ablated zinc binding and markedly impaired its inhibitory function, but left intact its ability to bind HLA-C and to transduce a positive signal through an immunoreceptor tyrosine-based activation motif grafted onto its cytoplasmic tail. Thus, zinc modulates specifically the negative signal transmitted by this KIR molecule. Mutation of an exposed amino-terminal zinc-binding motif alone was sufficient to impair the inhibitory function of KIR. The data suggest that complete inhibition of HLA-C-specific NK cells requires a zinc-dependent protein-protein interaction via the amino-terminal end of KIR2D.

Analysis of zinc binding sites in protein crystal structures

The geometrical properties of zinc binding sites in a dataset of high quality protein crystal structures deposited in the Protein Data Bank have been examined to identify important differences between zinc sites that are directly involved in catalysis and those that play a structural role. Coordination angles in the zinc primary coordination sphere are compared with ideal values for each coordination geometry, and zinc coordination distances are compared with those in small zinc complexes from the Cambridge Structural Database as a guide of expected trends. We find that distances and angles in the primary coordination sphere are in general close to the expected (or ideal) values. Deviations occur primarily for oxygen coordinating atoms and are found to be mainly due to H-bonding of the oxygen coordinating ligand to protein residues, bidentate binding arrangements, and multi-zinc sites. We find that H-bonding of oxygen containing residues (or water) to zinc bound histidines is almost universal in our dataset and defines the elec-His-Zn motif. Analysis of the stereochemistry shows that carboxyl elec-His-Zn motifs are geometrically rigid, while water elec-His-Zn motifs show the most geometrical variation. As catalytic motifs have a higher proportion of carboxyl elec atoms than structural motifs, they provide a more rigid framework for zinc binding. This is understood biologically, as a small distortion in the zinc position in an enzyme can have serious consequences on the enzymatic reaction. We also analyze the sequence pattern of the zinc ligands and residues that provide elecs, and identify conserved hydrophobic residues in the endopeptidases that also appear to contribute to stabilizing the catalytic zinc site. A zinc binding template in protein crystal structures is derived from these observations.

Genetically engineered zinc-chelating adenylate kinase from Escherichia coli with enhanced thermal stability

In contrast with adenylate kinase from Gram-negative bacteria, the enzyme from Gram-positive organisms harbors a structural Zn2+ bound to 3 or 4 Cys residues in the structural motif Cys-X2-Cys-X16-Cys-X2-Cys/Asp. Site-directed mutagenesis of His126, Ser129, Asp146, and Thr149 (corresponding to Cys130, Cys133, Cys150, and Cys153 in adenylate kinase from Bacillus stearothermophilus) in Escherichia coli adenylate kinase was undertaken for determining whether the presence of Cys residues is the only prerequisite to bind zinc or (possible) other cations. A number of variants of adenylate kinase from E. coli, containing 1-4 Cys residues were obtained, purified, and analyzed for metal content, structural integrity, activity, and thermodynamic stability. All mutants bearing 3 or 4 cysteine residues acquired zinc binding properties. Moreover, the quadruple mutant exhibited a remarkably high thermal stability as compared with the wild-type form with preservation of the kinetic parameters of the parent enzyme.

DNA repair enhancement by a combined supplement of carotenoids, nicotinamide, and zinc

Four volunteers were involved for 5 weeks of a baseline period, followed by 7 weeks of a combined supplementation of nicotinamide, zinc, and carotenoids (Nicoplex). Blood sampling and bioassays were carried out every week during the evaluation period. The supplementation of Nicoplex resulted in statistically significant increased resistance to DNA single-strand breaks induced by H2O2 (DNA retained on filter % from 46.7 +/- 1.9 to 59.4 +/- 4.3; p < 0.01), increased DNA repair 60 min after induction of damage (DNA retained on filter % from 74.6 +/- 4.8 to 88.3 +/- 4.2; p < 0.01), elevated poly (ADP-ribose) polymerase (PARP) activity (p < 0.05), and an increased proliferative response to phytohemagglutinin (PHA) (p < 0.05) when compared with the levels before supplementation. However, when the same subjects were supplemented with nicotinamide, zinc, and carotenoids together with another 17 nutrients or minerals, there were no changes in DNA damage, DNA repair, or proliferative response to PHA. Through the use of a rat model, DNA repair of splenocytes 3 h after 12 Gy whole-body irradiation was significantly enhanced in rats supplemented with Nicoplex for 6 weeks (p < 0.05) and 8 weeks (p < 0.01). Comparison of Nicoplex and its components administered separately revealed that there was an additive effect on DNA repair for both single- and double-strand breaks (both p < 0.05). On the basis of the results, it is hypothesized that the enhanced effect of combined supplement of nicotinamide, zinc, and carotenoids on DNA repair depends on their diversified mechanisms of action while multinutrient supplementation may compromise the effects by inhibitory interactions including uptake and absorption.

The gut-enriched Krüppel-like factor suppresses the activity of the CYP1A1 promoter in an Sp1-dependent fashion

The gut-enriched Krüppel-like factor (GKLF) is a newly identified zinc finger-containing transcription factor. Recent studies indicate that GKLF binds to a core DNA sequence of 5'-(G/A)(G/A)GG(C/T)G(C/T)-3', which is found in an endogenous cis element, the basic transcription element (BTE) of the cytochrome P-450IA1 (CYP1A1) promoter. The present study characterizes the ability of GKLF to regulate CYP1A1 expression. By electrophoretic mobility gel shift assay (EMSA) and methylation interference assay, GKLF was found to bind BTE in a manner similar to several other transcription factors known to interact with BTE including Sp1 and BTEB. Cotransfection studies in Chinese hamster ovary cells showed that GKLF inhibited the CYP1A1 promoter in a dose- and BTE-dependent manner. The same experiments also revealed that BTE was responsible for a significant portion of the CYP1A1 promoter activity. EMSA of nuclear extracts from Chinese hamster ovary cells showed that Sp1 and Sp3 were two major proteins that interacted with BTE. Additional cotransfection studies showed that GKLF inhibited Sp1-mediated activation of the CYP1A1 promoter. In contrast, GKLF enhanced Sp3-dependent suppression of the same promoter. Moreover, the ability of GKLF to inhibit Sp1-dependent transactivation was in part due to physical interaction of the two proteins. These findings indicate that GKLF is a negative regulator of the CYP1A1 promoter in a BTE-dependent fashion and that this inhibitory effect is in part mediated by physical interaction with Sp1.

Differential requirements for basic amino acids in transcription factor IIIA-5S gene interaction

Basic amino acids Arg, Lys, and His in the Cys2His2 zinc fingers of transcription factor IIIA (TFIIIA) potentially have important roles in factor binding to the extended internal control region (ICR) of the 5S ribosomal gene. Conserved and non-conserved basic residues in the N-terminal fingers I, II, III and the more C-terminal fingers V and IX were analyzed by site-directed mutagenesis and DNase I protection in order to assess their individual requirement in the DNA-binding mechanism. In the DNA recognition helix of finger II, the conserved Arg at position 62 (N-terminal side of the first zinc-coordinating histidine) was changed to a Leu or Gln. Both the R62L and R62Q mutations inhibited Xenopus TFIIIA-dependent DNase I footprinting along the entire 5S gene ICR. When His-58 (non-conserved basic residue with DNA-binding potential in the same helical region) was changed to a Gln, the mutated protein was able to protect the ICR from DNase I digestion. Therefore, Arg-62 is individually required for TFIIIA binding over the entire ICR whereas His-58 is not. Fingers V and IX have conserved Arg residues in positions identical to Arg-62 in finger II (Arg-154 in finger V and Arg-271 in finger IX). When these residues were changed to Leu and Ile respectively, TFIIIA-dependent DNase I protection was observed along the entire 5S gene ICR. These results indicate differing DNA-binding mechanisms by the N-terminal fingers versus the C-terminal fingers at the level of individual amino acid-nucleotide interactions. In the N-terminal finger I, the conserved Lys at position 11 outside the recognition helix and a conserved hydrophobic Trp at position 28 within the helix were changed to an Ala and Ser respectively. The K11A change inhibited TFIIIA-dependent DNase I protection to a much greater extent than the W28S change.

Specific RNA binding proteins constructed from zinc fingers

A zinc finger library with degenerate alpha-helices was displayed on the surface of bacteriophage and proteins that bind human immunodeficiency virus type-1 (HIV-1) Rev response element stem loop IIB (RRE-IIB) RNA or 5S rRNA were isolated. DNA encoding affinity selected zinc fingers was shuffled by recombination in vitro to isolate proteins with higher RNA binding affinity. Proteins constructed in this way bind RNA specifically both in vitro and in vivo. These results demonstrate that RNA substrate specificity of zinc fingers can be changed through mutation of alpha-helices to construct novel RNA binding proteins.

Identification of a family of zinc transporter genes from Arabidopsis that respond to zinc deficiency

Millions of people worldwide suffer from nutritional imbalances of essential metals like zinc. These same metals, along with pollutants like cadmium and lead, contaminate soils at many sites around the world. In addition to posing a threat to human health, these metals can poison plants, livestock, and wildlife. Deciphering how metals are absorbed, transported, and incorporated as protein cofactors may help solve both of these problems. For example, edible plants could be engineered to serve as better dietary sources of metal nutrients, and other plant species could be tailored to remove metal ions from contaminated soils. We report here the cloning of the first zinc transporter genes from plants, the ZIP1, ZIP2, and ZIP3 genes of Arabidopsis thaliana. Expression in yeast of these closely related genes confers zinc uptake activities. In the plant, ZIP1 and ZIP3 are expressed in roots in response to zinc deficiency, suggesting that they transport zinc from the soil into the plant. Although expression of ZIP2 has not been detected, a fourth related Arabidopsis gene identified by genome sequencing, ZIP4, is induced in both shoots and roots of zinc-limited plants. Thus, ZIP4 may transport zinc intracellularly or between plant tissues. These ZIP proteins define a family of metal ion transporters that are found in plants, protozoa, fungi, invertebrates, and vertebrates, making it now possible to address questions of metal ion accumulation and homeostasis in diverse organisms.

MOLECULAR BIOLOGY OF CATION TRANSPORT IN PLANTS

This review summarizes current knowledge about genes whose products function in the transport of various cationic macronutrients (K, Ca) and micronutrients (Cu, Fe, Mn, and Zn) in plants. Such genes have been identified on the basis of function, via complementation of yeast mutants, or on the basis of sequence similarity, via database analysis, degenerate PCR, or low stringency hybridization. Not surprisingly, many of these genes belong to previously described transporter families, including those encoding Shaker-type K+ channels, P-type ATPases, and Nramp proteins. ZIP, a novel cation transporter family first identified in plants, also seems to be ubiquitous; members of this family are found in protozoa, yeast, nematodes, and humans. Emerging information on where in the plant each transporter functions and how each is controlled in response to nutrient availability may allow creation of food crops with enhanced mineral content as well as crops that bioaccumulate or exclude toxic metals.

Efficacies of zinc-finger-active drugs against Giardia lamblia

Twenty-nine of 34 (85%) Zn-finger-active compounds at 300 microM or less inhibited the growth of Giardia lamblia. The most active compound, disulfiram (Antabuse), was cidal at 1.23 +/- 0.32 microM. In the adult mouse model, significant in vivo activity was demonstrated by increased cure rates and decreased parasite burdens.

Zinc status relates to hematological deficits in middle-aged women

OBJECTIVE

The objective of our study was to investigate zinc (Zn) status and the effects of Zn supplementation in relation to iron deficiency anemia in middle-aged women. It is important to define the role of Zn in hematologic abnormalities and to determine the frequency of Zn deficiency.

METHODS

Fifty-two Japanese women, selected from a health examination survey on 6200 women, had hemoglobin concentrations below 12.0 g/dl, total iron binding capacity (TIBC) below 390 micrograms/dl and fairly normocytemia. These 52 were divided into three groups and we then compared the hematological status before and after iron (group A) or Zn (group B) or iron plus Zn (group C) supplementation.

RESULTS

After treatment, concentrations of hemoglobin (Hb) increased slightly in groups A and B, but not statistically significant. In group C, Hb levels were significantly increased from 10.8 +/- 1.1 to 12.8 +/- 1.1 g/dl. Furthermore, numbers of RBC and reticulocytes, and concentrations of albumin were also increased significantly. Increased values over 1.0 g/dl of hemoglobin levels were noted in four women (26.6%) in group A, three women (14.2%) in group B and 13 women (81.2%) in group C.

CONCLUSION

Zn status to some extent can account for hematological abnormalities in middle-aged women. At least 5.0% of middle-aged Japanese women may have Zn deficiency. Normocytic anemia with low TIBC levels may serve as a good indicator of a marginal Zn deficiency.

Influenza virus NS1 protein interacts with the cellular 30 kDa subunit of CPSF and inhibits 3'end formation of cellular pre-mRNAs

Inhibition of the nuclear export of poly(A)-containing mRNAs caused by the influenza A virus NS1 protein requires its effector domain. Here, we demonstrate that the NS1 effector domain functionally interacts with the cellular 30 kDa subunit of CPSF, an essential component of the 3' end processing machinery of cellular pre-mRNAs. In influenza virus-infected cells, the NS1 protein is physically associated with CPSF 30 kDa. Binding of the NS1 protein to the 30 kDa protein in vitro prevents CPSF binding to the RNA substrate and inhibits 3' end cleavage and polyadenylation of host pre-mRNAs. The NS1 protein also inhibits 3' end processing in vivo, and the uncleaved pre-mRNA remains in the nucleus. Via this novel regulation of pre-mRNA 3' end processing, the NS1 protein selectively inhibits the nuclear export of cellular, and not viral, mRNAs.

The p95 gene of Bombyx mori nuclear polyhedrosis virus: temporal expression and functional properties

As part of our effort to identify baculovirus proteins acting as transcriptional regulators, we have characterized a gene, p95, of Bombyx mori nuclear polyhedrosis virus (BmNPV) that encompasses an open reading frame for a putative 95-kDa polypeptide (P95). The N-terminal half of the conceptually translated P95 contains two zinc finger-type DNA-binding motifs, and its C terminus contains a proline-rich region reminiscent of transcriptional activation regions. Northern blot analysis indicates that two mRNA species, 3.5 and 1.7 kb in size, are transcribed from the p95 gene at different times postinfection. These two mRNA species are produced by differential polyadenylation site usage. While the longer transcript can encode the P95 protein, the shorter one may encode a prematurely terminated version of the P95 polypeptide produced by ribosome frameshifting occurring at heptanucleotide "slippage" sites located near the relevant polyadenylation site. Transcription of the p95 gene is initiated at a proximal site located 70 nucleotides upstream of the translation start codon of P95, a middle site located 170 nucleotides from the start codon, and a set of three closely spaced distal sites located 385, 390, and 409 nucleotides from the translation start codon. The middle and distant initiation sites are utilized before and after BmNPV DNA replication, while transcripts initiated at the proximal site occur largely during the late and very late stages of viral infection. Transient-expression assays indicate that P95 can stimulate gene expression driven by the promoter of its own gene and the promoter of the cytoplasmic actin gene of B. mori. The P95-mediated trans activation can be further augmented by BmIE1, an immediate-early gene product of BmNPV. In contrast to the case with the actin promoter, however, the promoter of the p95 gene can be trans activated by the product of its own gene only in the presence of BmIE1. Our data suggest that proteins P95 and BmIE1 of BmNPV and, by analogy, those of other baculoviruses may interact with each other and synergize to potentiate transcription.

Agrobacterium transcriptional regulator Ros is a prokaryotic zinc finger protein that regulates the plant oncogene ipt

Virulence genes of Agrobacterium tumefaciens are under the control of positive and negative transcriptional regulators. We found that the transcriptional regulator Ros controls expression of the plant oncogene ipt, which encodes isopentenyl transferase, in A. tumefaciens. This enzyme is involved in biosynthesis of the plant growth hormone cytokinin in the host plant. An ipt promoter::cat reporter gene fusion showed a 10-fold increase in ipt promoter activity in A. tumefaciens ros mutant strains when compared with wild type. Also, increased levels (10- to 20-fold) of isopentenyl adenosine, the product of the reaction catalyzed by isopentenyl transferase, were detected in ros mutant strains. In vitro studies using purified Ros showed it binds directly to the ipt promoter. Analysis of the deduced Ros amino acid sequence identified a novel type of C2H2 zinc finger. In Ros the peptide loop spacing of the zinc finger is 9 amino acids as opposed to the invariant 12 amino acids in the classical C2H2 motif. Site-directed mutagenesis of Cys-82 and His-92 in this motif showed that these residues are essential for Zn2+ and DNA binding activities of Ros. The existence of such a regulator in Agrobacterium may be due to horizontal interkingdom retrotransfer of the ros gene from plant to bacteria.

Role of metal-ligand coordination in the folding pathway of zinc finger peptides

In the zinc fingers of TFIIIA family, two cysteines near the N-terminus and two histidines near the C-terminus are conserved for each finger unit. A cooperative binding of these residues to a Zn(II) ion is essential for the formation of the finger structure consisting of an anti-parallel beta-sheet and an alpha-helix. In order to reveal the folding pathway of the zinc finger, we have investigated, by Raman spectroscopy, the relationship between Zn(II)-ligand binding and conformational change of a 27-mer peptide representing the third finger of mouse transcription factor Zif268. In the absence of Zn(II), the peptide assumes a beta-sheet-rich structure. Upon addition of Zn(II), cysteines preferentially bind to Zn(II) prior to the metal coordination of histidines. Both the Zn(II)-cysteine and Zn(II)-histidine binding induce a partial secondary structure transition from beta-sheet to alpha-helix. Exchange of the ligand amino acid residues, i.e., cysteines to histidines and vice versa, produces a striking effect on the folding of the peptide. The beta-sheet-->alpha-helix transition is induced only by the Zn(II)-cysteine binding and the ligand exchanged peptide is not capable of folding into the finger structure. The present results demonstrate the importance of the ligand arrangement in the folding of zinc finger.

Inhibition of Friend virus replication by a compound that reacts with the nucleocapsid zinc finger: anti-retroviral effect demonstrated in vivo

The zinc finger structure that is found in the nucleocapsid protein of nearly all retroviruses has been proposed as a target for antiviral therapy. Since compounds that chemically attack the cysteines of the finger have been shown to inactivate both human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MuLV) in vitro, 14 of these compounds were tested in an MuLV-induced Friend disease model to assess their ability to inhibit retroviral replication in vivo. Of the 14 compounds tested, only Aldrithiol-2 clearly exhibited anti-retroviral activity as measured indirectly by the delay of Friend disease onset (P < 0.05). These results were confirmed by quantitative competitive polymerase chain reaction studies which monitored viral spread by measuring the level of viral DNA in the peripheral blood mononuclear cells of treated mice. Comparison of treated mice with untreated mice revealed that Aldrithiol-2 produced a greater than 2-log reduction in virus levels. These results functionally demonstrate that a zinc finger-attacking compound can inhibit viral replication in vivo. Since only 1 of the 14 compounds studied was effective, this study also shows the importance of in vivo testing of these types of antiviral compounds in an animal model. Given the strict conservation of the metal-coordinating cysteine structure within HIV-1 and MuLV zinc fingers, our results support the proposal that anti-retroviral drugs which target the nucleocapsid zinc finger may be clinically useful against HIV-1.

Zinc and brain injury

Zinc is an essential catalytic or structural element of many proteins, and a signaling messenger that is released by neural activity at many central excitatory synapses. Growing evidence suggests that zinc may also be a key mediator and modulator of the neuronal death associated with transient global ischemia and sustained seizures, as well as perhaps other neurological disease states. Manipulations aimed at reducing extracellular zinc accumulation, or cellular vulnerability to toxic zinc exposure, may provide a novel therapeutic approach toward ameliorating pathological neuronal death in these settings.

A20 Inhibits NF-κB Activation in Endothelial Cells Without Sensitizing to Tumor Necrosis Factor–Mediated Apoptosis

Expression of the NF-κB–dependent gene A20 in endothelial cells (EC) inhibits tumor necrosis factor (TNF)–mediated apoptosis in the presence of cycloheximide and acts upstream of IκBα degradation to block activation of NF-κB. Although inhibition of NF-κB by IκBα renders cells susceptible to TNF-induced apoptosis, we show that when A20 and IκBα are coexpressed, the effect of A20 predominates in that EC are rescued from TNF-mediated apoptosis. These findings place A20 in the category of “protective” genes that are induced in response to inflammatory stimuli to protect EC from unfettered activation and from undergoing apoptosis even when NF-κB is blocked. From a therapeutic perspective, genetic engineering of EC to express an NF-κB inhibitor such as A20 offers the mean of achieving an anti-inflammatory effect without sensitizing the cells to TNF-mediated apoptosis.

A20 Inhibits NF-κB Activation in Endothelial Cells Without Sensitizing to Tumor Necrosis Factor–Mediated Apoptosis

Expression of the NF-κB–dependent gene A20 in endothelial cells (EC) inhibits tumor necrosis factor (TNF)–mediated apoptosis in the presence of cycloheximide and acts upstream of IκBα degradation to block activation of NF-κB. Although inhibition of NF-κB by IκBα renders cells susceptible to TNF-induced apoptosis, we show that when A20 and IκBα are coexpressed, the effect of A20 predominates in that EC are rescued from TNF-mediated apoptosis. These findings place A20 in the category of “protective” genes that are induced in response to inflammatory stimuli to protect EC from unfettered activation and from undergoing apoptosis even when NF-κB is blocked. From a therapeutic perspective, genetic engineering of EC to express an NF-κB inhibitor such as A20 offers the mean of achieving an anti-inflammatory effect without sensitizing the cells to TNF-mediated apoptosis.