Identification of an oxidative refolding intermediate of recombinant consensus interferon from inclusion bodies and design of a two-stage strategy to promote correct disulfide-bond formation.

Dilution refolding of recombinant consensus IFN (interferon) from inclusion bodies suffers from low yield. A stable intermediate was found to mix with the correct product and to have an antiviral activity of less than 10% of the latter. This intermediate would form precipitates upon removal of the precipitation inhibitor arginine. Compared with the native protein, the intermediate moved more slowly on non-reducing SDS/PAGE. The CD and fluorescence spectra indicated that it had formed a native-like structure, but had only one disulfide bond: Cys(29)-Cys(139). Further evidence showed that the formation of Cys(29)-Cys(139) is specific and very likely to happen, even in the presence of a high concentration of reducing agent, whereas pairing of the other disulfide (Cys(1)-Cys(99)) needed a stronger oxidative condition. It competed with intermolecular disulfide bonding to form covalent oligomers. On the basis of this discovery, a two-stage refolding step strategy was designed that employed a modified dilution refolding step followed by a dialysis refolding step. The first stage used a high concentration of reducing agent together with the precipitation inhibitor arginine. The purpose was to hinder any reaction through Cys(1) or Cys(99) but allow the intramolecular disulfide bonding of Cys(29)-Cys(139). The second stage was a dialysis step that gradually increased the oxidative agent concentration and simultaneously decreased the arginine concentration. The refolding yield was increased from 35 to 82%, while the mass recovery was increased from 60 to 96%. Moreover, this strategy could suppress precipitation even after arginine was completely removed.