Rat interleukin-10: production and characterisation of biologically active protein in a recombinant bacterial expression system

Interleukin-10 is an anti-inflammatory Th1 immunosuppressive cytokine, the active form of which is a non-covalent homodimer, and which exhibits species-specificity both with respect to structure and biological activity. The rat homologue of IL-10 shares 73% identity with human IL-10 at the amino-acid sequence level, and has, in addition to the two disulphide bonds present in human IL-10, a fifth, unpaired cysteine (cys-149). Preparation of rat IL-10 by Bacterial expression followed by solubilisation and refolding in a glutathione redox system, results in a molecule in which cys-149 is almost entirely oxidised, existing either as disulphide dimer or as a mixed disulphide with glutathione, and which has less than 1% of the activity of the native (cys-149-SH) form of the molecule. Site directed mutagenesis of rat IL-10 to replace cys-149 with tyrosine produces a molecule which readily adopts the active conformation upon solubilisation and refolding, and which is recoverable in good yield from Bacterial expression systems. Comparison of the biological activities of rat IL-10tyr149 and commercial rat IL-10 preparations confirms that the activity of native-sequence rat IL-10 is either reduced or absent. It is proposed therefore that the biosynthetic analogue rat IL-10tyr149 is a more useful molecule to investigate the biological actions of IL-10 in the rat.