Starting from the primary structure of sunflower trypsin inhibitor SFTI-1, we designed novel non-covalent inhibitors of human and yeast 20S proteasomes. Peptides with Arg residue in P1 position and two basic amino acid residues (Lys or/and Arg) in P2′ and P3′ positions strongly inhibited chymotrypsin-like and caspase-like activities, while trypsin-like activity was poorly modified. We found that some SFTI-1 analogues up-regulated exclusively the chymotrypsin-like activity of latent yeast 20S proteasome.

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Preptin is a 34-amino-acid-long peptide derived from the E-domain of a precursor of insulin-like growth factor 2 (pro-IGF2) with bone-anabolic and insulin secretion amplifying properties. Here, we describe the synthesis,...

Sunflower trypsin inhibitor (SFTI-1) is recognized as an attractive scaffold to designed potent inhibitors of various proteases. We have recently found that its analogues inhibit noncovalently both human and yeast 20S proteasomes. Here, a set of novel and more potent in vitro inhibitors is presented. The inhibitory potency of the peptides was assessed with human 20S proteasome in the presence or absence of sodium dodecyl sulfate and with human 26 proteasome. Their antiproliferative action against tumor (human melanoma cells A375) and normal cells (46 BR.1N human fibroblasts and HaCaT keratinocytes) was determined. The selected fluoresceine-labeled inhibitors were able to internalize into A375 cells and were sometimes present as foci in the cells. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 685-696, 2016.

Isothermal titration calorimetry (ITC) technique was used to study the interactions of trypsin with bicyclic sunflower-derived trypsin inhibitor (SFTI-1) as well as with its new monocyclic (with disulphide bridge only) analogues (C 3 H 5 O)-SFTI-1 and (C 8 H 15 O)-SFTI-1. ITC measurements were run in 50 mM buffer solution of HEPES or Tricine of pH 8, containing 20 mM CaCl 2 at 298.15 K. Based on calorimetric data, the equilibrium constants for the inhibitor-enzyme-binding processes, K, the binding stoichiometry, N (inhibitor-to-enzyme molar ratio), as well as thermodynamic parameters (DG, DH, DS) for the reactions were determined. The study revealed that the stoichiometry of the resulting complexes equals 1:1. The negative binding enthalpy (D ITC H) and favourable entropy factor (TD ITC S) suggest an important contribution of hydrogen bonding as well as hydrophobic interactions to the inhibitor-enzyme affinity. Furthermore, the relationship between the modification of the peptide structure, the experimental conditions and the thermodynamic parameters has been discussed.