Characterization of recombinant mustard trypsin inhibitor 2 (MTI2) expressed in Pichia pastoris. 
The mustard trypsin inhibitor MTI2 was expressed as secretory protein in the yeast Pichia pastoris.  In order to evaluate the influence of the C-terminal amino acids of the precursor form on the inhibitor activity, the C-terminal precursor and the mature protein were both expressed.  A third His-tagged construct was also designed to compare alternative purification procedures.  Proteins were efficiently expressed at levels of 40-160 mg/l in shake flasks.  Equilibrium dissociation constants demonstrated that the mature protein was a stronger inhibitor of bovine beta-trypsin compared to the precursor and His-tagged forms (0.01 nM vs. 0.58 nM and 0.71 nM, respectively).  The recombinant proteins were active inhibitors of Spodoptera exigua gut proteases.