Résumé
BnD22, a protein shown to accumulate in
Brassica napus leaves adapted to progressive drought stress and to salinity, was previously found to be related to the Künitz protease inhibitor family. It was purified to homogeneity by high performance liquid chromatography and characterized by circular dichroism and mass spectrometry. The protein was shown to undergo a post-translational C-terminal cleavage of 22±1 amino acid residues proving that mature BnD22 is indeed a 19 kD holoprotein without side chain post-translational modification. Complementary to the sequence homology, BnD22 was found to be homologous to protease inhibitors with regards to its secondary structure and size. A negative correlation between the endogenous proteolytic activity in leaves adapted to progressive drought and the presence of BnD22 was established. The antiproteolytic activity of the purified mature BnD22 was assayed both on endogenous leaf proteases and purified serine proteases. A low level of antiproteolytic activity was observed, with a limited range of specificity. BnD22, nevertheless, might be involved in the decrease of the protease activity in the drought-adapted leaves, thus contributing to delay the leaf senescence.