Nucellins, plant aspartic proteases specifically expressed in nucellar cells during degradation.
Nucellins are important regulators of nucellar cell's progressive degradation after ovule fertilization. This degradation is a characteristic of programmed cell death. Nucellins are plant aspartic proteases specifically expressed in nucellar cells during degradation. The enzyme is characterized by having two aspartic protease catalytic site motifs, the 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. Aspartic proteases are bilobal enzymes, 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.
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