In silico screening of novel inhibitors of M17 Leucine Amino Peptidase (LAP) of Plasmodium vivax as therapeutic candidate.

M17 LAP (Leucine Amino Peptidase) plays an important role in the hydrolysis of amino acids essential for growth and development of Plasmodium vivax (Pv), the pathogen causing malaria. In this paper a homology model of PvLAP was generated using MODELLER v9.15. From different in-silico methods such as structure based, ligand based and de novo drug designing a total of 90 compounds were selected for docking studies. A final list of 10 compounds was prepared. The study reported the identification of 2-[(3-azaniumyl-2-hydroxy-4-phenylbutanoyl) amino]-4-methylpentanoate as the best inhibitor in terms of docking score and pharmacophoric features. The reliability of the binding mode of the inhibitor is confirmed by molecular dynamics (MD) simulation study with GROMACS software for a simulation time of 20ns in water environment. Finally, in silico ADMET analysis of the inhibitors using MedChem Designer v3 evaluated the drug likeness of the best hits to be considered for industrial pharmaceutical research.

Molecular Characterization of Babesia bovis M17 Leucine Aminopeptidase and Inhibition of Babesia Growth by Bestatin.

The M17 leucine aminopeptidase (M17LAP) enzymes of the other apicomplexan parasites have been characterized and shown to be inhibited by bestatin. Though Babesia bovis also belongs to the apicomplexan group, it is not known whether its M17LAP could display similar biochemical properties as well as inhibition profile. To unravel this uncertainty, a B. bovis M17LAP (BbM17LAP) gene was expressed in Escherichia coli , and activity of the recombinant enzyme as well as its inhibition by bestatin were evaluated. The inhibitory effect of the compound on growths of B. bovis and Babesia gibsoni in vitro was also determined. The expression of the gene fused with glutathione S-transferase (GST) yielded approximately 81-kDa recombinant BbM17LAP (rBbM17LAP). On probing with mouse anti-rBbM17LAP serum, a green fluorescence was observed on the parasite cytosol on confocal laser microscopy, and a specific band greater than the predicted molecular mass was seen on Western blotting. The Km and Vmax values of the recombinant enzyme were 139.3 ± 30.25 and 64.83 ± 4.6 µM, respectively, while the Ki was 2210 ± 358 µM after the inhibition. Bestatin was a more potent inhibitor of the growth of B. bovis [IC50 (50% inhibition concentration) = 131.7 ± 51.43 µM] than B. gibsoni [IC50 = 460.8 ± 114.45 µM] in vitro. The modest inhibition of both the rBbM17LAP activity and Babesia parasites' growth in vitro suggests that this inhibition may involve the endogenous enzyme in live parasites. Therefore, BbM17LAP may be a target of bestatin, though more studies with other aminopeptidase inhibitors are required to confirm this.

Unusual activity pattern of leucine aminopeptidase inhibitors based on phosphorus containing derivatives of methionine and norleucine.

Ligands containing bulky aliphatic P1 residues exhibit a high affinity towards cytosolic leucine aminopeptidase, a bizinc protease of biomedical significance. According to this specificity, a series of phosphonic and phosphinic compounds have been put forward as novel putative inhibitors of the enzyme. These phosphonic and phosphinic compounds were derivatives of methionine and norleucine as both single amino acids and dipeptides. The designed inhibitors were synthesised and tested towards the peptidase isolated from porcine kidneys using an improved separation procedure affording superior homogeneity. Unexpectedly, organophosphorus derivatives of methionine and norleucine exhibited moderate activity with K(i) values in the micromolar range.

Chitosan citrate as multifunctional polymer for vaginal delivery. Evaluation of penetration enhancement and peptidase inhibition properties.

In the present work the employment of chitosan citrate (Chs citrate) as multifunctional polymer in vaginal applications was evaluated. Potential properties of penetration enhancement and protease inhibition could be expected because of the capability of citrate to bind divalent cations such as calcium, that is involved in the regulation of gap and tight junctions, and zinc, that is essential co-factor for some proteases. A comparison was performed with chitosan HCl (Chs HCl). Ex vivo drug permeation experiments were performed on pig vaginal mucosa, by application of 3.0% (w/w) chitosan gels. Acyclovir (5.0%, w/w) and ciprofloxacin HCl (0.3%, w/w) were used as low molecular weight model drugs. Fluorescein isothiocyanate dextran MW 4400 (FD4) was used as hydrophilic high molecular weight fluorescent probe (0.2%, w/w). In the case of low MW drugs the amount penetrated into pig vaginal mucosa was measured by extraction from tissue slices and HPLC detection. From the samples maintained in contact with FD4, slices were cut perpendicularly to the surface and observed by means of confocal laser scanning microscopy (CLSM). FD4 permeation was also measured in in-vitro cell culture model (Caco-2). The penetration enhancing capacity of Chs citrate was comparable to that of Chs HCl. Both Chs citrate and Chs HCl were tested for the inhibition of the proteolytic enzymes carboxypeptidase A and leucine aminopeptidase. In both cases Chs citrate showed a significantly higher inhibition of enzymatic activity with respect to Chs HCl.

Molecular characterization of a puromycin-insensitive leucyl-specific aminopeptidase, PILS-AP.

The family M1 of Zn-dependent aminopeptidases comprises members of closely related enzymes which are known to be involved in a variety of physiologically important processes. On the basis of two highly conserved peptide motifs, we have identified a new member of this family by PCR amplification and cDNA-library screening. The longest ORF encodes a protein of 930 residues. It contains the HEXXH(X)18E Zn-binding motif and displays high homology to the other M1 family members except for its N-terminus for which a signal sequence of 20 residues can be predicted. This interpretation was supported by expressing fusion proteins formed with green fluorescent protein which localized to intracellular vesicles in COS-7 and BHK cells. Northern-blot analysis revealed ubiquitous expression of a major 3. 1-kb transcript. For enzymatic studies, the complete protein was expressed in Sf 9 insect cells. When aminoacyl beta-naphthylamides were used as substrates, efficient hydrolysis was only observed for Leu (and to a lesser extent Met). The activity was inhibited by chelators of bivalent cations and by other known aminopeptidase inhibitors, but surprisingly puromycin was without effect. This newly identified puromycin-insensitive leucyl-specific aminopeptidase is a signal-sequence-bearing member of family M1 and may be another example of the small subset of substrate-specific peptidases.

Biologically active triterpene saponins from Bupleurum fruticosum.

Extracts of the root of B. fruticosum L. showed in a biological screening hemolytical activity, hepatoprotective and phagocytosis stimulating effects, and a specific inhibitory activity of leucine aminopeptidase. Further monitoring of the fraction with antihepatotoxic activity led to the isolation of an hepatoprotective saikosaponin identified as buddlejasaponin IV and the new malonylbuddlejasaponin IV, determined as saikogenin F-3-O-[6-O-malonyl-beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl (1-->3)]-beta-D-fucopyranoside. The structures were elucidated on the basis of the chemical and spectroscopic data.

Leucine aminopeptidase from Arabidopsis thaliana. Molecular evidence for a phylogenetically conserved enzyme of protein turnover in higher plants.

Leucine aminopeptidases are exopeptidases which are presumably involved in the processing and regular turnover of intracellular proteins; however, their precise function in cellular metabolism remains to be established. Towards this goal, a full-length complementary DNA encoding a plant leucine aminopeptidase was isolated from a cDNA library of Arabidopsis thaliana and sequenced. The nucleotide sequence showed 49.5% identity to the Escherichia coli xerB-encoded leucine aminopeptidase. Sequence analysis revealed that the cDNA encodes a polypeptide of 520 amino acids with a calculated molecular mass of 54,506 Da. The C-terminal part (amino acids 200-520) of the deduced amino acid sequence showed 43.8% sequence identity to the xerB-encoded leucine aminopeptidase and 42.6% sequence identity to the amino acid sequence of bovine lens leucine aminopeptidase (EC 3.4.11.1). No sequence similarity (not even over short sequence elements) was observed with any other known peptidase or proteinase sequence. The cDNA was expressed as a fusion protein from the lacZ promoter in E. coli. Enzymatic analysis proved that the cloned cDNA encoded an active leucine aminopeptidase. The properties of this enzyme, including metal requirements, inhibitor sensitivity, pH optimum and the remarkable temperature stability, are very similar to those reported for leucine aminopeptidases from other tissues. Amino acids involved in metal and substrate binding in bovine lens aminopeptidase are completely conserved in the plant enzyme as well as in the XerB protein. Our results show that leucine aminopeptidases form a superfamily of highly conserved enzymes, spanning the evolutionary period from the bacteria to animals and higher plants. This is the first aminopeptidase cloned from a plant.

Tyromycin A: a novel inhibitor of leucine and cysteine aminopeptidases from Tyromyces lacteus.

Tyromycin A, a new inhibitor of leucine and cysteine aminopeptidases has been isolated from mycelial cultures of the basidiomycete Tyromyces lacteus (Fr.) Murr. Its structure was established as 1,16-bis-[4-methyl-2,5-dioxo-3-furyl]hexadecane (1) by spectral analysis and transformation into ester and imide derivatives.

Phosphorus amino acid analogues as inhibitors of leucine aminopeptidase.

A variety of phosphorus amino acid and dipeptide analogues have been synthesized and evaluated as inhibitors of the metalloenzyme leucine aminopeptidase from porcine kidney. Two phosphonate dipeptides were found to be modest inhibitors of the enzyme (8e, Ki = 58 microM; 8h, Ki = 340 microM). The phosphinic acid (17-OH) and phosphinamide (17-NH2) analogues related to bestatin were prepared by condensation of the phosphinate amino acid derivative 11, via a trivalent phosphonite ester 12, with leucine isocyanate derivatives 13. These compounds also proved to be unexceptional in their inhibition of LAP (17-O-, Ki = 56 microM; 17-NH2, Ki = 40 microM). A series of simple (alpha-aminoalkyl)phosphonic acid and -phosphinic acids were also evaluated, and the most potent inhibitors were found to be the phosphonic acid analogues of L-Leu and L-Phe [R)-3e, Ki = 0.23 microM; (R)-3h, Ki = 0.42 microM). Slow-binding behavior was observed for (R)-3e (kon = 400 +/- 55 M-1 s-1) and (R)-3h (kon = 445 +/- 50 M-1 s-1). The phosphinic acid analogues of Leu and Phe are 100-fold less potent than the phosphonate derivatives. The fact that tetrahedral phosphorus analogues are less potent inhibitors of LAP than they are of other zinc peptidases suggests that the mechanism of LAP may be fundamentally different than that of the latter enzymes.

Mitogenic potentials of bestatin, amastatin, arphamenines A and B, FK-156 and FK-565 on spleen lymphocytes.

The following aminopeptidase (AP) activities were found to be associated with the surface of mouse spleen cells: Leu-AP (138 pmol/10(5) cells X minute) and AP-B (16 pmol/10(5) cells X minute with Lys-beta-naphthylamide as substrate and 21 pmol/10(5) cells X minute with Arg-beta-naphthylamide substrate); AP-A activity was not detected by the assay system applied. The immunoactive peptide bestatin inhibited the Leu-AP, while AP-B activity decreased in the presence of both arphamenines A and B and bestatin. No effects on these enzymes were caused by amastatin (an AP-A inhibitor), FK-156, FK-565 and Bu-2743E; the latter peptide turned out to be not an inhibitor of cell surface associated microsomal Leu-AP but an inhibitor of cytosolic Leu-AP. The immunoactive peptides bestatin, arphamenines A and B, and amastatin increased [3H]thymidine incorporation into spleen cells containing lymphocytes and macrophages. These mitogenic actions were not observed when macrophages were removed from the cultures or the cells had been stimulated with ConA or LPS. The lactoyl- and heptanoyl peptides FK-156 and FK-565 caused a mitogenic action on lymphocytes independently of the presence of macrophages. The inhibitor of cytosolic Leu-AP did not change the incorporation into lymphocytes.