InterPro domain: IPR033823

Nucellin (MEROPS identifier A01.073) is an important regulator of a nucellar cell's progressive degradation after ovule fertilization. This degradation is a characteristic of programmed cell death. Nucellin is a plant aspartic endopeptidase specifically expressed in nucellar cells during degradation [ 1 , 2 ]. The enzyme is characterized by having two aspartic endopeptidase catalytic site motifs, Asp-Thr-Gly-Ser in the N-terminal and Asp-Ser-Gly-Ser in the C-terminal region, and two other regions nearly identical to two regions of plant aspartic proteases. An aspartic endopeptidase is a bilobal enzyme, with each lobe contributing a catalytic Asp residue, with an extended active site cleft localized between the two lobes of the molecule. One lobe may be evolved from the other through ancient gene-duplication event. Although the three-dimensional structures of the two lobes are very similar, the amino acid sequences are more divergent, except for the conserved catalytic site motif [ 3 ].

This entry represents the peptidase domain of nucellin.

1. Molecular organization of a gene in barley which encodes a protein similar to aspartic protease and its specific expression in nucellar cells during degeneration. Plant Mol. Biol. 35, 821-31
2. The rice nucellin gene ortholog OsAsp1 encodes an active aspartic protease without a plant-specific insert and is strongly expressed in early embryo. Plant Cell Physiol. 46, 87-98