Modification of Escherichia coli B glutathione synthetase with polyethylene glycol for clinical application to enzyme replacement therapy for glutathione deficiency

Modification of thiol functionalized aptamers by conjugation of synthetic polymers

Aptamers are known for their short in vivo circulating half-life and rapid renal clearance. Their conjugation to poly(ethylene glycol) (PEG) is a way to improve their residence in the body. Two aptamers (AptD and AptF), having a disulfide protected thiol modification on the 3' end, have been conjugated to maleimide activated PEGs of various molecular weights and structures (linear PEG20; branched PEG20 and 40; PolyPEG17, 40, and 60 kDa). The high yield coupling (70-80% in most of the cases) could be achieved using immobilized tris[2-carboxyethyl]phosphine hydrochloride (TCEP) as reducing agent at pH 4. The affinity of PEGylated AptD for its target was reduced by conjugation to linear PEG20 and branched PEG40, but not to branched PEG20 and PolyPEGs. This work demonstrates an alternative approach to PEGylation of aptamers, and that the effect of PEG on the affinity for the target varies according to the structure and conformation of the synthetic polymer.

Modification of allergenicity and immunogenicity of formate dehydrogenase by conjugation with linear mono methoxy poly ethylene glycol: Improvement in detoxification of formate in methanol poisoning

BACKGROUND

Single bolus intravenous infusion of native formate dehydrogenase (FD), isolated from Candida boidinii was found to eliminate formate, a highly toxic metabolite in methanol poisoning. In order to prevent immunological reactions which might be produced by multiple dosing of formate dehydrogenase and to prolong the serum half life of the enzyme, the N-hydroxysuccinimidyl ester of methoxy polyethylene glycol propionic acid (mPEG-SPA 5000) was conjugated to native formate dehydrogenase.

METHOD

PEGylation reactions were run at 20 degrees C for 30 min in a reaction buffer (0.2 mol/l sodium phosphate buffer, pH 8.3). The PEGylated molecules were purified from unreacted PEG with Amicon Ultra-4 (10 K) and by Sephacryl S-300 HR gel-filtration chromatography. Unreacted formate dehydrogenase molecules were removed by DEAE Sepharose FF anion-exchange chromatography. PEG-FD enzyme molecules obtained from reacting ratio of FD/PEG of 1/40 had an enzyme activity of 68% of unmodified enzyme. Immunogenicity of PEGylated and native enzyme was evaluated by ELISA. Allergenicity was evaluated by active systemic anaphylaxis and passive cutaneous anaphylaxis tests. In vivo efficacy of PEG-FD or native FD was comparatively evaluated by single intravenous administration of PEG-FD or native FD in folate deficient methanol intoxicated albino rats along with Carbicarb buffer infusion. Methanol and formate were estimated at specific time points respectively with HPLC and fluorescence spectrophotometer.

RESULT

PEG-FD had comparatively longer half life and lower immunogenicity than native FD. PEG-FD had better in vivo efficacy than native FD in eliminating the formate.

CONCLUSION

Conjugation of mPEG-SPA 5000 with native FD reduces its immunogenicity and increases its efficacy in detoxification of formate in methanol poisoning.

The Yap1p-dependent induction of glutathione synthesis in heat shock response of Saccharomyces cerevisiae

Glutathione is synthesized in two sequential reactions catalyzed by gamma-glutamylcysteine synthetase (GSH1 gene product) and glutathione synthetase (GSH2 gene product). The expression of GSH1 in Saccharomyces cerevisiae has been known to be up-regulated by Yap1p, a critical transcription factor for the oxidative stress response in yeast. The present study demonstrates that GSH2 expression is also regulated by Yap1p under oxidative stress-induced conditions. In addition to oxidative stress, expression of GSH1 and GSH2 was induced by heat shock stress in a Yap1p-dependent manner with subsequent increases in intracellular glutathione content. Oxygen respiration rate increased when cells were exposed to higher temperatures, and as a result, intracellular oxidation levels were increased. The heat shock-induced expression of GSH1 and GSH2 did not occur under anaerobic conditions. Furthermore, even under aerobic conditions, the heat shock response of these genes was not observed when cells were pretreated with KCN to block oxygen respiration. We speculate that heat shock stress enhances oxygen respiration, which in turn results in an increase in the generation of reactive oxygen species in mitochondria. This signal may be mediated by Yap1p, resulting in the elevation of intracellular glutathione levels.

Molecular identification of glutathione synthetase (GSH2) gene from Saccharomyces cerevisiae

The hypothetical protein YOL049w on the chromosome XV was identified to be the structural gene for glutathione synthetase (GSH2) of Saccharomyces cerevisiae. Translational initiation site was identified by making the GSH2-lacZ fusion. The GSH2 gene contained an open reading frame (1473 bp) with 491 amino acids, and molecular weight of the GSH2 gene product was calculated to be 55,812. Glutathione synthetase activity in transformant carrying the GSH2 gene with multicopy plasmid increased approximately 4-fold. The GSH2 gene was not essential for growth of yeast cell, and glutathione was not detected from the gsh2 disrupter.