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Two isoforms of Saccharomyces cerevisiae glutaredoxin 2 are expressed in vivo and localize to different subcellular compartments.

ABSTRACT: Glutaredoxin (Grx)2 from Saccharomyces cerevisiae is a member of the two-cysteine (dithiol) subfamily of Grxs involved in the defence against oxidative stress in yeast. Recombinant yeast Grx2p, expressed in Escherichia coli, behaves as a 'classical' Grx that efficiently catalyses the reduction of hydroxyethyl disulphide by GSH. Grx2p also catalyses the reduction of GSSG by dihydrolipoamide with even higher efficiency. Western blot analysis of S. cerevisiae crude extracts identifies two isoforms of Grx2p of 15.9 and 11.9 kDa respectively. The levels of these two isoforms reach a peak during the exponential phase of growth in normal yeast extract/peptone/dextrose ('YPD') medium, with the long form predominating over the short one. From immunochemical analysis of subcellular fractions, it is shown that both isoforms are present in mitochondria, but only the short one is detected in the cytosolic fraction. On the other hand, only the long form is prominent in microsomes. Mitochondrial isoforms should represent the processed and unprocessed products of an open reading frame (YDR513W), with a putative start codon 99 bp upstream of the GRX2 start codon described thus far. These results indicate that GRX2 contains two in-frame start codons, and that translation from the first AUG results in a product that is targeted to mitochondria. The cytosolic form would result either by initiation from the second AUG, or by differential processing of one single translation product.

SUBMITTER: Pedrajas JR

PROVIDER: S-EPMC1222607 | biostudies-other | 2002 Jun

REPOSITORIES: biostudies-other

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Project description:BACKGROUND: Protein subcellular localization and differences in oxidation state between subcellular compartments are two well-studied features of the the cellular organization of S. cerevisiae (yeast). Theories about the origin of subcellular organization are assisted by computational models that can integrate data from observations of compositional and chemical properties of the system. PRESENTATION AND IMPLICATIONS OF THE HYPOTHESIS: I adopt the hypothesis that the state of yeast subcellular organization is in a local energy minimum. This hypothesis implies that equilibrium thermodynamic models can yield predictions about the interdependence between populations of proteins and their subcellular chemical environments. TESTING THE HYPOTHESIS: Three types of tests are proposed. First, there should be correlations between modeled and observed oxidation states for different compartments. Second, there should be a correspondence between the energy requirements of protein formation and the order the appearance of organelles during cellular development. Third, there should be correlations between the predicted and observed relative abundances of interacting proteins within compartments. RESULTS: The relative metastability fields of subcellular homologs of glutaredoxin and thioredoxin indicate a trend from less to more oxidizing as mitochondrion - cytoplasm - nucleus. Representing the overall amino acid compositions of proteins in 23 different compartments each with a single reference model protein suggests that the formation reactions for proteins in the vacuole (in relatively oxidizing conditions), ER and early Golgi (in relatively reducing conditions) are relatively highly favored, while that for the microtubule is the most costly. The relative abundances of model proteins for each compartment inferred from experimental data were found in some cases to correlate with the predicted abundances, and both positive and negative correlations were found for some assemblages of proteins in known complexes. CONCLUSION: The results of these calculations and tests suggest that a tendency toward a metastable energy minimum could underlie some organizational links between the the chemical thermodynamic properties of proteins and subcellular chemical environments. Future models of this kind will benefit from consideration of additional thermodynamic variables together with more detailed subcellular observations.

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Two isoforms of Saccharomyces cerevisiae glutaredoxin 2 are expressed in vivo and localize to different subcellular compartments.

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