Purification and characterization of recombinant Streptomyces clavuligerus isopenicillin N synthase produced in Escherichia coli

Recombinant isopenicillin N synthase from Streptomyces clavuligerus was produced in the form of inactive inclusion bodies in Escherichia coli. These inclusion bodies were solubilized by treatment with 5 M urea under reducing conditions. Optimization of refolding conditions to recover active isopenicillin N synthase indicated that a dialysis procedure carried out at a protein concentration of about 1.0 mg ml(-1) gave maximal recovery of active isopenicillin N synthase. Solubilized isopenicillin N synthase of more than 95% purity was obtained by passing this material through a DEAE-Trisacryl ion exchange column. Expression studies conducted at different temperatures indicated that isopenicillin N synthase was produced predominantly in a soluble, active form when expression was conducted at 20 degrees C, and accounted for about 20% of the total soluble protein. This high-level production facilitated the purification of soluble isopenicillin N synthase to near homogeneity in four steps. Characterization of the purified soluble and solubilized isopenicillin N synthase revealed that they are very similar.