Production and purification of TAL6003: a novel version of the protease plasmin.

TAL6003 is an engineered form of human plasmin under development for thrombolytic therapy. TAL6003 (38.2kDa) contains nine disulfide bonds distributed within and between its two functional domains, a 25.2 kDa serine protease domain linked to a 13.0 kDa kringle I domain; kringles 2-5 present in native human plasmin have been deleted from this plasmin molecule. TAL6003 is expressed as its zymogen in Escherichia coli and is harvested in inclusion bodies. Following solubilization of inclusion bodies with urea as the chaotrope and glutathione as the reducing agent, this zymogen is refolded by dilution to a final concentration of 0.5mg/ml, with a yield of 48% (relative to total zymogen). Refolded TAL6003 zymogen is filtered, diafiltered, and filtered again prior to capture and purification on SP Sepharose, which is highly effective in removing host-cell protein. Subsequent affinity purification on ECH-Lysine Sepharose serves to capture polypeptide chains containing correctly refolded kringle 1 domain, which is the locus of the molecule's lysine-binding site, and to further eliminate host-cell protein. TAL6003 zymogen eluted from the ECH-Lysine Sepharose column is activated to TAL6003 with streptokinase, with an activity yield of approximately 80%. Proteolytically active TAL6003 is stripped of streptokinase by passage through an anion-exchange (Q) membrane and is then affinity purified on Benzamidine Sepharose, which serves to remove unreacted TAL6003 zymogen and proteolytically degraded TAL6003. An ultrafiltration/diafiltration step, to concentrate and to formulate TAL6003, completes the purification process. The final product exhibited a specific activity of close to unity and high purity by several relevant criteria.

Inhibition of Mrp2- and Ycf1p-mediated transport by reducing agents: evidence for GSH transport on rat Mrp2.

Mammalian Mrp2 and its yeast orthologue, Ycf1p, mediate the ATP-dependent cellular export of a variety of organic anions. Ycf1p also appears to transport the endogenous tripeptide glutathione (GSH), whereas no ATP-dependent GSH transport has been detected in Mrp2-containing mammalian plasma membrane vesicles. Because GSH uptake measurements in isolated membrane vesicles are normally carried out in the presence of 5-10 mM dithiothreitol (DTT) to maintain the tripeptide in the reduced form, the present study examined the effects of DTT and other sulfhydryl-reducing agents on Ycf1p- and Mrp2-mediated transport activity. Uptake of S-dinitrophenyl glutathione (DNP-SG), a prototypic substrate of both proteins, was measured in Ycf1p-containing Saccharomyces cerevisiae vacuolar membrane vesicles and in Mrp2-containing rat liver canalicular plasma membrane vesicles. Uptake was inhibited in both vesicle systems in a concentration-dependent manner by DTT, dithioerythritol, and beta-mercaptoethanol, with concentrations of 10 mM inhibiting by approximately 40%. DTT's inhibition of DNP-SG transport was noncompetitive. In contrast, ATP-dependent transport of [(3)H]taurocholate, a substrate for yeast Bat1p and mammalian Bsep bile acid transporters, was not significantly affected by DTT. DTT also inhibited the ATP-dependent uptake of GSH by Ycf1p. As the DTT concentration in incubation solutions containing rat liver canalicular plasma membrane vesicles was gradually decreased, ATP-dependent GSH transport was now detected. These results demonstrate that Ycf1p and Mrp2 are inhibited by concentrations of reducing agents that are normally employed in studies of GSH transport. When this inhibition was partially relieved, ATP-dependent GSH transport was detected in rat liver canalicular plasma membranes, indicating that both Mrp2 and Ycf1p are able to transport GSH by an ATP-dependent mechanism.