Expression of Recombinant Hirudin in Bacteria and Yeast: A Comparative Approach

The expression of recombinant proteins in heterologous hosts is a common strategy to obtain larger quantities of the "protein of interest" (POI) for scientific, therapeutic or commercial purposes. However, the experimental success of such an approach critically depends on the choice of an appropriate host system to obtain biologically active forms of the POI. The correct folding of the molecule, mediated by disulfide bond formation, is one of the most critical steps in that process. Here we describe the recombinant expression of hirudin, a leech-derived anticoagulant and thrombin inhibitor, in the yeast <i>Komagataella phaffii</i> (formerly known and mentioned throughout this publication as <i>Pichia pastoris</i>) and in two different strains of <i>Escherichia coli</i>, one of them being especially designed for improved disulfide bond formation through expression of a protein disulfide isomerase. Cultivation of the heterologous hosts and expression of hirudin were performed at different temperatures, ranging from 22 to 42 °C for the bacterial strains and from 20 to 30 °C for the yeast strain, respectively. The thrombin-inhibitory potencies of all hirudin preparations were determined using the thrombin time coagulation assay. To our surprise, the hirudin preparations of <i>P. pastoris</i> were considerably less potent as thrombin inhibitors than the respective preparations of both <i>E. coli</i> strains, indicating that a eukaryotic background is not per se a better choice for the expression of a biologically active eukaryotic protein. The hirudin preparations of both <i>E. coli</i> strains exhibited comparable high thrombin-inhibitory potencies when the strains were cultivated at their respective optimal temperatures, whereas lower or higher cultivation temperatures reduced the inhibitory potencies.