Purification, Characterization, and Antimicrobial Activity Against <i>Candida parapsilosis</i> and <i>Staphylococcus aureus</i> of a Highly Stable Type-1 Cystatin from Terminalia catappa L. Seeds

The inhibitor was purified by heating the crude extract at 80°C for 30 min, followed by ion exchange chromatography on a DEAE cellulose column. The purification index was 9-fold, yielding 2.3%. SDS-PAGE and size exclusion chromatography revealed that the protease inhibitor (<i>Tc</i>PI) is a 15.9 kDa monomeric protein. The inhibition kinetics showed that <i>Tc</i>PI is a competitive inhibitor specific to papain (Ki = 1.02 x 10^-4 M). <i>Tc</i>PI remained active even after heating at 100oC for 120 min and at pH conditions varying from 2.0 to 10.0. Even after 60 min, <i>Tc</i>PI was resistant to papain proteolysis. <i>Tc</i>PI exhibited antimicrobial activity against <i>Candida parapsilosis</i> and <i>Staphylococcus aureus.</i> Conclusion: Here, we show that <i>Tc</i>PI is a highly stable type-1 cystatin with the potential to combat infections caused by <i>C. parapsilosis</i> and <i>S. aureus</i>. Additional investigations into <i>Tc</i>PI's structural aspects and mechanism of action, as well as safety assessments, are essential prerequisites for its potential application as a novel therapeutic intervention.