Expression of a TGF-beta superfamily protein, macrophage inhibitory cytokine-1, in the yeast Pichia pastoris.

The methylotrophic yeast, Pichia pastoris, has been used to express both human and murine macrophage inhibitory cytokine-1 (MIC-1), a transforming growth factor beta (TGF-beta) superfamily cytokine. This is the first report of the expression of a correctly folded TGF-beta superfamily protein in a microbial organism. The protein is secreted in its correctly folded dimeric form at milligram per litre quantities, which are significantly higher than we have been able to achieve using mammalian expression systems. Purification schemes are described, and the purified protein is immunologically identical to protein produced in a mammalian expression system. Protein expression was influenced by a number of factors, most significantly by the concentration of methanol used during the induction phase. However, with very high levels of MIC-1 induction, substantial amounts of MIC-1 monomer were also secreted.