SjAPI, the first functionally characterized Ascaris-type protease inhibitor from animal venoms

Area of Science:

• Biochemistry
• Toxicology
• Molecular Biology

Background:

• Serine protease inhibitors modulate serine proteases and protect venom peptides from degradation.
• Known animal venom protease inhibitors are exclusively Kunitz-type, leaving the existence of other types unexplored.

Purpose of the Study:

• To identify and characterize novel types of protease inhibitors in animal venom.
• To investigate the functional and structural properties of newly discovered Ascaris-type protease inhibitors.

Main Methods:

• Screening of scorpion venom gland cDNA libraries.
• Biochemical characterization of the Ascaris-type peptide SjAPI.
• Enzyme kinetics experiments to determine inhibitory properties.
• Bioinformatics analyses and chimera experiments.

Main Results:

• Identification of the first Ascaris-type animal toxin family with four members (SjAPI, SjAPI-2, CtAPI, BmAPI).
• Detailed characterization of SjAPI, a 64-residue peptide with five disulfide bridges, distinct from known venom protease inhibitors.
• Recombinant SjAPI demonstrated dual inhibitory activity against α-chymotrypsin (Ki = 97.1 nM) and elastase (Ki = 3.7 μM).
• SjAPI possesses unique

Conclusions:

• SjAPI represents the first functionally characterized animal toxin peptide with an Ascaris-type fold.
• The discovery highlights the structural and functional diversity of venom toxins.
• Animal venom glands are a promising source for novel protease inhibitors for diagnostic and therapeutic applications.