Phytaspase
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Phytaspase is a member of the plant subtilisin-like protease family, and is commonly distinguished from the other members by its unusual and extremely high specificity towards its substrates, which resembles that of the animal caspases. Similarly to the animal caspases, the phytaspase is a cell death promoting protease.[1]
The name phytaspase comes from phyto- (greek. for plant) and -aspase (aspartate-directed protease), similarly to caspases.
Substrate specificity
The phytaspase displays a strict substrate specificity, which resembles that of the animal caspase-3.[2] It recognizes a tetrapetide motive within a target protein and introduces a peptide bond break following an aspartate residue, which is crucial for the hydrolysis. Theoretical speculations, based on a 3D model predictions have been made, pointing to the histidine 331 of the phytaspase peptide chain, that might interact with the Asp in the target peptide and thereby guide the recognition.[3]
Structure
The phytaspase displays a structure, common to the subtilisin-like proteases.[4] Its N-terminus includes a prodomain, which commonly inhibits subtilisin-like proteases[5] and undergoes an autocatalytic cleavage during maturation,[6] followed by a protease domain, which includes and adheres the common order of the sequence of the three canonic catalytic amino acid residues,[7] and a prolonged C-terminal domain.