Dual hydrolytic role for Pb(II) ions

Microarray analysis of differential gene expression in lead-exposed astrocytes

The toxic metal lead is a widespread environmental health hazard that can adversely affect human health. In an effort to better understand the cellular and molecular consequences of lead exposure, we have employed cDNA microarrays to analyze the effects of acute lead exposure on large-scale gene expression patterns in immortalized rat astrocytes. Our studies identified many genes previously reported to be differentially regulated by lead exposure. Additionally, we have identified novel putative targets of lead-mediated toxicity, including members of the family of calcium/phospholipid binding annexins, the angiogenesis-inducing thrombospondins, collagens, and tRNA synthetases. We demonstrate the ability to distinguish lead-exposed samples from control or sodium samples solely on the basis of large-scale gene expression patterns using two complementary clustering methods. We have confirmed the altered expression of candidate genes and their encoded proteins by RT-PCR and Western blotting, respectively. Finally, we show that the calcium-dependent phospholipid binding protein annexin A5, initially identified as a differentially regulated gene by our microarray analysis, is directly bound and activated by nanomolar concentrations of lead. We conclude that microarray technology is an effective tool for the identification of lead-induced patterns of gene expression and molecular targets of lead.

Structural analysis of the P10/11-P12 RNA domain of yeast RNase P RNA and its interaction with magnesium

The P10/11-P12 RNA domain of yeast RNase P contains several highly conserved nucleotides within a conserved secondary structure. This RNA domain is essential for enzyme function in vivo, where it has a demonstrated role in divalent cation utilization. To better understand the function of this domain, its structure and alterations in response to magnesium have been investigated in vitro. A secondary structure model of the P10/11-P12 RNA domain had been previously developed by phylogenetic analysis. Computer modeling and energy minimization were applied to the Saccharomyces cerevisiae P10/11-P12 domain to explore alternatives and additional interactions not predicted by the phylogenetic consensus. The working secondary structure models were challenged with data obtained from 1H NMR and in vitro chemical and enzymatic probing experiments. The solution structure of the isolated domain was found to conform to the phylogenetic prediction within the context of the holoenzyme. Structure probing data also discriminated among additional base contacts predicted by energy minimization. The withdrawal of magnesium does not appear to cause gross refolding or rearrangement of the RNA domain structure. Instead, subtle changes occur in the solution accessibility of specific nucleotide positions. Most of the conserved nucleotides reported to be involved in magnesium utilization in vivo also display magnesium-dependent changes in vitro.