Castor bean cake contains a trypsin inhibitor that displays antifungal activity against Colletotrichum gloeosporioides and inhibits the midgut proteases of the dengue mosquito larvae

• A castor cake trypsin inhibitor (RcTI) was purified and characterized.
• RcTI is a competitive inhibitor with a dissociation constant (Ki) of 1.9 × 10−5 mM.
• The trypsin inhibitory activity of RcTI was stable after heat and pH treatments.
• RcTI inhibits the spore germination of Colletotrichum gloeosporioides.
• RcTI inhibits Aedes aegypti larval midgut proteases.

A novel trypsin inhibitor, named RcTI, was purified from castor bean cake (Ricinus communis L.) by heat treatment followed by chromatography on anhydrotrypsin-Sepharose 4B and Resource Q. RcTI is a 14 kDa competitive inhibitor with pI 5.2 and a dissociation constant (Ki) of 1.9 × 10−5 mM. The amino-terminal sequence showed similarity with a 2S sulfur-rich seed storage protein (83%) and napin-like protein (48%). RcTI was stable over a broad pH range and is exceptionally resistant to heating as it retained high inhibitory activity toward trypsin after incubation at 100 °C for 2 h. RcTI (13 μg) inhibited the spore germination of the phytopatogenic fungus Colletotrichum gloeosporioides and promoted 91% inhibition of the proteases from the midgut of Aedes aegypti larvae. The results of the present study indicate that RcTI has biotechnological potential as an alternative agent to combat the important phytopathogen C. gloeosporioides and the larvae of A. aegypti.