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

Introduction: Clinic infections caused by various microorganisms are a public health concern. The rise of new strains resistant to traditional antibiotics has exacerbated the problem. Thus, the search for new antimicrobial molecules remains highly relevant.

Methods: The current study purified, characterized, and assessed the antimicrobial activity of a papain inhibitor from Terminalia catappa L. seeds.

Results: 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 (TcPI) is a 15.9 kDa monomeric protein. The inhibition kinetics showed that TcPI is a competitive inhibitor specific to papain (Ki = 1.02 x 10-4 M). TcPI remained active even after heating at 100 ºC for 120 min and at pH conditions varying from 2.0 to 10.0. Even after 60 min, TcPI was resistant to papain proteolysis. TcPI exhibited antimicrobial activity against Candida parapsilosis and Staphylococcus aureus.

Conclusion: Here, we show that TcPI is a highly stable type-1 cystatin with the potential to combat infections caused by C. parapsilosis and S. aureus. Additional investigations into TcPI's structural aspects and mechanism of action, as well as safety assessments, are essential prerequisites for its potential application as a novel therapeutic intervention.