Co-overexpression of folding modulators improves the solubility of the recombinant guinea pig liver transglutaminase expressed in Escherichia coli

Transglutaminases (EC 2.3.2.13) catalyze the formation of epsilon-(gamma-glutamyl)lysine cross-links and the substitution of primary amines for the gamma-carboxamide groups of protein bound glutamine residues, and are involved in many biological phenomena. Transglutaminase reactions are also applicable in applied enzymology. Here, we established an expression system of recombinant mammalian tissue-type transglutaminase with high productivity. Overexpression of guinea pig liver transglutaminase in Escherichia coli, using a plasmid pET21-d, mostly resulted in the accumulation of insoluble and inactive enzyme protein. By the expression culture at lower temperatures (25 and 18 degrees C), however, a fraction of the soluble and active enzyme protein slightly increased. Co-overexpression of a molecular chaperone system (DnaK-DnaJ-GrpE) and/or a folding catalyst (trigger factor) improved the solubility of the recombinant enzyme produced in E. coli cells. The specific activity, the affinity to the amine substrate, and the sensitivity to the calcium activation and GTP inhibition of the purified soluble recombinant enzyme were lower than those of the natural liver enzyme. These results indicated that co-overexpression of folding modulators tested improved the solubility of the overproduced recombinant mammalian tissue-type transglutaminase, but the catalytic properties of the soluble recombinant enzyme were not exactly the same as those of the natural enzyme.