Protein-rich fraction of Cnidoscolus urens (L.) Arthur leaves: enzymatic characterization and procoagulant and fibrinogenolytic activities.

Proteolytic enzymes are important macromolecules in the regulation of biochemical processes in living organisms. Additionally, these versatile biomolecules have numerous applications in the industrial segment. In this study we have characterized a protein-rich fraction of Cnidoscolus urens (L.) Arthur leaves, rich in proteolytic enzymes, and evaluated its effects on the coagulation cascade. Three protein-rich fractions were obtained from the crude extract of C. urens leaves by precipitation with acetone. Fraction F1.0 showed higher proteolytic activity upon azocasein, and thus, was chosen for subsequent tests. The proteolytic activity of F1.0 on fibrinogen was dose-dependent and time-dependent. The extract demonstrated procoagulant activity on citrated plasma and reduced the APTT, not exerting effects on PT. Despite the fibrin(ogen)olytic activity, F1.0 showed no defibrinogenating activity in vivo. The fraction F1.0 did not express hemorrhagic nor hemolytic activities. The proteolytic activity was inhibited by E-64, EDTA and in the presence of metal ions, and increased when pretreated with reducing agents, suggesting that the observed activity was mostly due to cysteine proteases. Several bands with proteolytic activity were detected by zymography with gelatin, albumin and fibrinogen. The optimal enzymatic activity was observed in temperature of 60 °C and pH 5.0, demonstrating the presence of acidic proteases. In conclusion, these results could provide basis for the pharmacological application of C. urens proteases as a new source of bioactive molecules to treat bleeding and thrombotic disorders.

Structural and mechanistic insights into a novel non-competitive Kunitz trypsin inhibitor from Adenanthera pavonina L. seeds with double activity toward serine- and cysteine-proteinases.

Kunitz proteinase inhibitors are widely distributed in legume seeds, and some of them have the ability to inhibit two different classes of enzymes. In this report, novel insights into three-dimensional structure and action mechanism of ApKTI, an Adenanthera pavonina Kunitz trypsin inhibitor, were provided to shed some light on an unconventional non-competitive activity against trypsin and papain. Firstly, ApKTI was purified by two tandem-size molecular exclusion chromatography high resolutions, Sephacryl S-100 and Superose 12 10/300 GL. Purified ApTKI showed molecular mass of 22 kDa and higher affinity against trypsin in comparison to papain, while the bifunctional inhibitor presented lower inhibitory activity. Moreover, in vitro assays showed that ApKTI has two independent interaction sites, permitting simultaneous inhibition to both enzymes. Theoretical three-dimensional structures of ApTKI complexed to both target proteinases were constructed in order to determine interaction mode by using Modeller v9.6. Since the structure of no non-competitive Kunitz inhibitor has been elucidated, ApTKI-trypsin and ApTKI-papain docking were carried out using Hex v5.1. In silico experiments showed that the opposite inhibitor loop interacts with adjacent sites of trypsin (Arg(64), Ser(107), Arg(88) and Lys(108)) and papain (Gln(51), Asp(172) and Arg(173)), probably forming a ternary complex. Unusual residue substitutions at the proposed interface can explain the relative rarity of twin trypsin/papain inhibition. The predicted non-coincidence of trypsin and papain binding sites is completely different from that of previously proposed inhibitors, adding more information about mechanisms of non-competitive plant proteinase inhibitors.