Sulfur Sparing in the Yeast Proteome in Response to Sulfur Demand

Abstract

Genome-wide studies have recently revealed the unexpected complexity of the genetic response to apparently simple physiological changes. Here, we show that when yeast cells are exposed to Cd(2+), most of the sulfur assimilated by the cells is converted into glutathione, a thiol-metabolite essential for detoxification. Cells adapt to this vital metabolite requirement by modifying globally their proteome to reduce the production of abundant sulfur-rich proteins. In particular, some abundant glycolytic enzymes are replaced by sulfur-depleted isozymes. This global change in protein expression allows an overall sulfur amino acid saving of 30%. This proteomic adaptation is essentially regulated at the mRNA level. The main transcriptional activator of the sulfate assimilation pathway, Met4p, plays an essential role in this sulfur-sparing response.

The Yeast Ubiquitin Ligase SCFMet30Regulates Heavy Metal Response

“…These experiments demonstrated up-regulation of proteins involved in the sulfur amino acid biosynthesis pathway, indicating the need to replace damaged proteins containing the sulfur amino acids methionine and cysteine. Interestingly, similar studies that analyzed the response to hydrogen peroxide-induced oxidative stress showed a striking difference between the cadmium and the oxidative stress response because a small decrease of sulfur amino acid pathway components was observed in response to hydrogen peroxide (Godon et al, 1998).Cadmium exposure of yeast also induces expression of several isozymes of the carbohydrate metabolism such as pyruvate decarboxylase, enolase, and aldehyde dehydrogenase (Fauchon et al, 2002). All the cadmium-induced isozymes showed markedly reduced sulfur content, that is, less methionine and cysteine residues compared with the enzymes expressed under nonstress conditions.…”

“…Rather than by direct DNA damage, cadmium leads to genome instability by inhibition of the DNA mismatch repair system (Jin et al, 2003). Although the mechanism of how cadmium inhibits DNA repair is not clear, it has been suggested that damage of sulfhydryl groups containing components of the mismatch repair system might be responsible (Jin et al, 2003).The damaging effect of cadmium on sulfhydryl groups containing proteins also is reflected in gene expression profiling experiments and proteome analyses in response to cadmium exposure (Vido et al, 2001;Fauchon et al, 2002). These experiments demonstrated up-regulation of proteins involved in the sulfur amino acid biosynthesis pathway, indicating the need to replace damaged proteins containing the sulfur amino acids methionine and cysteine.…”

“…In addition, the isozyme switch may protect the carbohydrate metabolism because the sulfur-poor isozymes are predicted to be less cadmium sensitive than their sulfur-rich counterparts (Fauchon et al, 2002;Jamieson, 2002). Both isozyme switching and induction of sulfur amino acid synthesis pathway components in response to cadmium exposure have been shown to depend primarily on the yeast transcription factor Met4 (Fauchon et al, 2002). Microarray analysis showed that cadmium-dependent induction of Ͼ60 genes was severely affected in ⌬met4 mutants (Fauchon et al, 2002 (Kuras et al, 1996) and the DNA-binding factors Cbf1 (Kuras et al, 1997), Met31, and Met32 (Blaiseau et al, 1997).…”

Assessing factors for reliable quantitative proteomics based on two‐dimensional gel electrophoresis

“…The first dimension separation can be performed with either carrier ampholites or immobilized pH gradients. Proteins may be stained with chemical dyes (such as Coomassie Blue [12][13] or silver nitrate [14]), labelled with radioactive isotopes ( 3 H, 14 C, 35 S, 32 P) [15][16][17], or revealed by fluorography. Using phosphor screen technology, one can label differently the proteome in two different conditions by growing cells on two isotope media, such as 3 H and 35 S [18], or 3 H and 14 C [19], and compare the relative values of each signal.…”

“…Similarly, the difference gel electrophoresis (DIGE [20]) is based on the differential incorporation of two fluorescent cyanine dyes. Various software packages have been developed for protein quantification [21], and have been used to study a large range of biological processes in various species, such as physiological changes due to environmental stress [15][16][17]22] or to development [12,14]. In genetics, proteins have been used to reveal variability between species [23] or genotypes [12][13][24][25][26].…”