Production and Purification of Recombinant Hirudin Expressed in the Methylotrophic YeastPichia pastoris

A recombinant form of hirudin (HIR), a potent thrombin inhibitor derived from the leechHirudo medicinalis,was cloned and expressed in the methylotrophic yeastPichia pastoris.The HIR gene was inserted into theP. pastorispPic9K expression vector such that the gene's expression is under alcohol oxidase (AOX1) promoter control and the HIR coding sequence is fused to theSaccharomyces cerevisiaepre-pro α-mating factor signal sequence. ATn903Kan^rdeterminant andHis4⁺gene are also present on pPic9K, affording a method for selecting chromosomal integrants of the HIR gene. Following electroporation of the DNA into theP. pastorisstrain GS115 (his-4), His⁺transformants were recovered and plated on medium containing increasing concentrations of the aminoglycoside antibiotic G418. The resulting His⁺G418-resistant transformants were grown in shake flasks and screened for those that secreted recombinant hirudin (rHIR) to the growth medium. Clones exhibiting rHIR production and secretion were retained for fermentation studies where optimization of growth conditions was found to dramatically increase rHIR expression. One clone that was retained for further characterization secreted rHIR at a level of 1.5 g/liter. Using a straightforward two-step chromatography procedure, the rHIR was purified to >97% with a recovery yield of 63%. The purified rHIR had the predicted N-terminal amino acid sequence and exhibited the same thrombin inhibition kinetics as a variety of HIR isoforms produced in other heterologous systems. Based on these data,P. pastorisoffers an efficient system for production and purification of multigram quantities of biologically active rHIR for structure/function analyses.