InterPro domain: IPR033165

Legumain beta (MEROPS identifier C13.001) is a cysteine endopeptidase that cleaves proteins at asparaginyl bonds. Legumain beta is found only in plants and has been biochemically characterized from the jack bean (Canavalia ensiformis) [ 1 ]. Cleavage of aspartyl bonds can occur, but bonds are cleaved much more slowly [ 2 ]. The enzyme is synthesized as a precursor and autolytic activation occurs at aspartyl bonds releasing N- and C-terminal propeptides [ 3 ]. The enzyme is located in the plant vacuole, is maximally active at pH 5.0-5.5 and processes seed storage proteins including albumin and globulin precursors [ 4 ]. Seed storage proteins are activated during seed maturation and not during germination [ 5 ]. Legumains are also required for programmed cell death in plants in which vacuolar collapse follows vacuole membrane disruption leading to release of the vacuolar enzymes into the cytoplasm. This occurs as a defence strategy during viral and fungal infections [ 6 , 7 ], but also during seed development [ 8 ].

1. Asparaginyl endopeptidase of jack bean seeds. Purification, characterization, and high utility in protein sequence analysis. J. Biol. Chem. 268, 3525-9
2. Legumain forms from plants and animals differ in their specificity. Biol. Chem. 382, 953-9
3. Vacuolar processing enzyme is self-catalytically activated by sequential removal of the C-terminal and N-terminal propeptides. FEBS Lett. 447, 213-6
4. A unique vacuolar processing enzyme responsible for conversion of several proprotein precursors into the mature forms. FEBS Lett. 294, 89-93
5. Vacuolar processing enzymes are essential for proper processing of seed storage proteins in Arabidopsis thaliana. J. Biol. Chem. 278, 32292-9
6. A plant vacuolar protease, VPE, mediates virus-induced hypersensitive cell death. Science 305, 855-8
7. Vacuolar processing enzyme is essential for mycotoxin-induced cell death in Arabidopsis thaliana. J. Biol. Chem. 280, 32914-20
8. A vacuolar processing enzyme, deltaVPE, is involved in seed coat formation at the early stage of seed development. Plant Cell 17, 876-87