In the present study the structural properties of potato protease inhibitor 1 (PI-1) were studied as afunction of temperature to elucidate its precipitation mechanism upon heating. A cDNA coding forPI-1 from cv. Bintje was cloned and expressed in
Pichia pastoris. Using the recombinant PI-1 it wassuggested that PI-1 behaves as a hexameric protein rather than as a pentamer, as previously proposedin the literature. The recombinant protein seems either to have a predominantly unordered structureor to belong to the
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-II proteins. Differential scanning calorimetry analysis of PI-1 revealed that itsthermal unfolding occurs via one endothermic transition in which the hexameric PI-1 probably unfolds,having a dimer instead of a monomer as cooperative unit. The transition temperature for therecombinant PI-1 was 88
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C. Similar results were obtained for a partially purified pool of native PI-1from cv. Bintje.Keywords: Potato;
Solanum tuberosum; protease inhibitor;
Pichia pastoris; recombinant PI-1