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Biopolymers. 2013 Mar 11. doi: 10.1002/peps.22231. [Epub ahead of print]

Mechanism-based selection of a potent kallikrein-related peptidase 7 inhibitor from a versatile library based on the sunflower trypsin inhibitor SFTI-1.

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Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, 4059, Australia.


Potent and specific enzyme inhibition is a key goal in development of therapeutic inhibitors targeting proteolytic activity. The backbone-cyclised peptide, Sunflower Trypsin Inhibitor (SFTI-1) affords a scaffold that can be engineered to achieve both these aims. SFTI-1's mechanism of inhibition is unusual in that it shows fast-on/slow-off kinetics driven by cleavage and religation of a scissile bond. This phenomenon was used to select a nanomolar inhibitor of kallikrein related peptidase 7 (KLK7) from a versatile library of SFTI variants with diversity tailored to exploit distinctive surfaces present in the active site of serine proteases. Inhibitor selection was achieved through use of size exclusion chromatography to separate protease/inhibitor complexes from unbound inhibitors followed by inhibitor identification according to molecular mass ascertained by mass spectrometry. This approach identified a single dominant inhibitor species with molecular weight of 1562.4 Da, which is consistent with the SFTI variant SFTI-WCTF. Once synthesised individually this inhibitor showed an IC50 of 173.9±7.6 nM against chromogenic substrates and could block protein proteolysis. Molecular modelling analysis suggested that selection of SFTI-WCTF was driven by specific aromatic interactions and stabilised by an enhanced internal hydrogen bonding network. This approach provides a robust and rapid route to inhibitor selection and design. © 2013 Wiley Periodicals, Inc. Biopolymers, 2013.

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