Binding at the interface: We tested the inhibitory activity of a set of peptide sequences derived from an α-helix of the dimeric trypanothione reductase from Leishmania infantum. Replacement of a glutamic acid residue with a lysine promoted monomer dissociation and enzyme inhibition.

A series of 9-mer and 13-mer amide-bridged cyclic peptides derived from the linear prototype Ac-PKIIQSVGIS-Nle-K-Nle-NH (Toro et al. ChemBioChem2013) has been designed and synthesized by introduction of the lactam between amino acid side chains that are separated by one helical turn (i, i+4). All of these compounds were tested in vitro as both dimerization and enzyme inhibitors of Leishmania infantum trypanothione reductase (Li-TryR). Three of the 13-mer cyclic peptide derivatives (3, 4 and 6) inhibited the oxidoreductase activity of Li-TryR in the low micromolar range and they also disrupted enzyme dimerization. Cyclic analogues 3 and 4 were more resistant to proteases than was the linear prototype. Furthermore, the most potent TryR inhibitors in the linear and cyclic series displayed potent in vitro activity against Leishmania infantum upon conjugation with cationic cell-penetrating peptides. To date, these conjugated peptides can be considered the first example of TryR dimerization inhibitors that are active in cell culture.

A series of new selenocyanates and diselenides bearing interesting bioactive scaffolds (quinoline, quinoxaline, acridine, chromene, furane, isosazole, etc.) was synthesized, and their in vitro leishmanicidal activities against Leishmania infantum amastigotes along with their cytotoxicities in human THP-1 cells were determined. Interestingly, most tested compounds were active in the low micromolar range and led us to identify four lead compounds (1h, 2d, 2e, and 2f) with 50% effective dose (ED 50 ) values ranging from 0.45 to 1.27 M and selectivity indexes of >25 for all of them, much higher than those observed for the reference drugs. These active derivatives were evaluated against infected macrophages, and in order to gain preliminary knowledge about their possible mechanism of action, the inhibition of trypanothione reductase (TryR) was measured. Among these novel structures, compounds 1h (3,5-dimethyl-4-isoxazolyl selenocyanate) and 2d [3,3=-(diselenodiyldimethanediyl)bis(2-bromothiophene)] exhibited good association between TryR inhibitory activity and antileishmanial potency, pointing to 1h, for its excellent theoretical ADME (absorption, distribution, metabolism, and excretion) properties, as the most promising lead molecule for leishmancidal drug design.

Characteristics and functional efficacy of digestive proteases of Catla catla, catla, Labeo rohita, rohu and Hypophthalmichthys molitrix, silver carp were studied. Total protease activity was significantly (P < 0.05) higher in rohu (1.219 ± 0.059 U mg protein )1 min )1 ) followed by silver carp (1.084 ± 0.061 U mg protein )1 min )1 ), and catla (0.193 ± 0.006 U mg protein )1 min )1 ). Trypsin activity of silver carp and rohu was 89-91% higher than catla. Chymotrypsin activity was significantly (P < 0.05) higher in silver carp compared with rohu and catla. The protease activity of rohu and silver carp displayed bell-shaped curves with maximum activity at pH 9; whereas in catla, maximum activity was found between pH 8 and 11. Inhibition of protease activity with soybean trypsin inhibitor (SBTI), phenylmethylsulfonyl fluoride (PMSF) revealed the presence of serine proteases and inhibition of activity with N-a-p-tosyl-L-lysine-chloromethyl ketone (TLCK) and N-tosyl-L-phenylalanychloromethane (TPCK) indicated the presence of trypsin-like and chymotrypsin-like enzymes in all these three carps. SDS-PAGE showed the presence of several protein bands ranging from 15.3 to 121.9 kDa in enzyme extracts of catla, rohu and silver carp. The substrate SDS-PAGE evidenced the presence of various protease activity bands ranging from 21. 6-93.7, 21.6-63.8 and 26.7-98.5 kDa for catla, rohu and silver carp respectively. In pH-stat hydrolysis of Chilean fishmeal showed significantly (P < 0.05) higher degree of hydrolysis compared with soybean meal, silver cup (a commercial fish feed of Mexico) and wheat flour, with enzyme preparations of three fishes. The rate of hydrolysis was significantly (P < 0.05) higher in silver carp compared with others. KEY WORDS

The objective of the current study was to enhance the proteolytic stability of peptide-based inhibitors that target critical protein-protein interactions at the dimerization interface of Leishmania infantum trypanothione reductase (Li-TryR) using a backbone modification strategy. To achieve this goal we carried out the synthesis, proteolytic stability studies and biological evaluation of a small library of α/β-peptide foldamers of different length (from 9-mers to 13-mers) and different α→β substitution patterns related to prototype linear α-peptides. We show that several 13-residue α/β-peptide foldamers retain inhibitory potency against the enzyme (in both activity and dimerization assays) while they are far less susceptible to proteolytic degradation than an analogous α-peptide. The strong dependence of the binding affinities for Li-TryR on the length of the α,β-peptides is supported by theoretical calculations on conformational ensembles of the resulting complexes. The conjugation of the most proteolytically stable α/β-peptide with oligoarginines results in a molecule with potent activity against L. infantum promastigotes and amastigotes.