High Variability of Phytaspase Proteolytic Activity in Plants of Various Species: Possible Implications

Phytaspases are plant proteases involved in stress-induced plant cell death. They share substrate specificity with animal apoptotic proteases (caspases) and exhibit high selectivity toward their protein substrates. Rice phytaspase has previously been shown to hydrolyze, and thereby inactivate, the heterologous protein human gastrin, a peptide hormone. Because reducing gastrin levels may be beneficial in several human pathological conditions, we compared phytaspase activity across a wide range of edible plants. Phytaspase activity varied by one to two orders of magnitude, even among closely related plant species. We isolated and identified phytaspase from pepper fruits (Capsicum annuum), one of the plant materials with the highest activity, produced the recombinant enzyme, and characterized some of its biochemical properties, including substrate specificity. We further demonstrated that pepper phytaspase efficiently hydrolyzes human gastrin in vitro. These findings support further experimental investigation of the hypothesis that consuming pepper may reduce gastrin levels in the human body.