P-I class metalloproteinase from Bothrops moojeni venom is a post-proline cleaving peptidase with kininogenase activity: insights into substrate selectivity and kinetic behavior

Snake venom metalloproteinases (SVMPs) belonging to P-I class are able to hydrolyze extracellular matrix proteins and coagulation factors triggering local and systemic reactions by multiple molecular mechanisms that are not fully understood. BmooMPα-I, a P-I class SMVP from Bothrops moojeni venom, was active upon neuro- and vaso-active peptides including angiotensin I, bradykinin, neurotensin, oxytocin and substance P. Interestingly, BmooMPα-I showed a strong bias towards hydrolysis after proline residues, which is unusual for most of characterized peptidases. Moreover, the enzyme showed kininogenase activity similar to that observed in plasma and cells by kallikrein. FRET peptide assays indicated a relative promiscuity at its S2-S'2 subsites, with proline determining the scissile bond. This unusual post-proline cleaving activity was confirmed by the efficient hydrolysis of the synthetic combinatorial library MCA-GXXPXXQ-EDDnp, described as resistant for canonical peptidases, only after Pro residues. Structural analysis of the tripeptide LPL complexed with BmooMPα-I, generated by molecular dynamics simulations, assisted in defining the subsites and provided the structural basis for subsite preferences such as the restriction of basic residues at the S2 subsite due to repulsive electrostatic effects and the steric impediment for large aliphatic or aromatic side chains at the S1 subsite. These new functional and structural findings provided a further understanding of the molecular mechanisms governing the physiological effects of this important class of enzymes in envenomation process.

Releasing or expression modulating mediator involved in hemostasis by Berythractivase and Jararhagin (SVMPs)

PIII snake venom metalloproteases (SVMPs) are structurally related to ADAMs (a disintegrin and metalloprotease human family of proteins). Berythractivase and Jararhagin are PIII SVMPs with 69% homology with different hemostatic properties. In order to clarify these differences and further characterize the biological effects of these proteins, we compared the effect of both proteases on human umbilical vein endothelial cell (HUVEC) for evaluating the release and modulation of coagulation and fibrinolysis mechanisms as well as the expression of their correlated genes. We found that both proteins increase the von Willebrand factor liberation, but did not modulate gene expression. Berythractivase, differently from Jararhagin increased the expression of tissue factor. Our results showed that both SVMPs (Berythractivase and Jararhagin) activate HUVEC releasing or modulating mediators involved in hemostasis. Meanwhile, we can suggest through the up-regulation of TF gene that the studied SVMP acts in a specific manner, suggesting that Jararhagin has preferentially a local action, while Berythractivase can be assumed as a systemic pro-coagulant protein with activity on the surface of HUVECs.

High molecular weight kininogen as substrate for cathepsin B

We investigated the influence of pH and divalent cations (Zn2+, Mg2+ and Ca2+) on high molecular weight kininogen processing by cathepsin B. At pH 6.3, high molecular weight kininogen is hydrolyzed by cathepsin B at three sites generating fragments of 80, 60 and 40 kDa. Cathepsin B has kininogenase activity at this pH which is improved in the absence of divalent cations. At pH 7.35, high molecular weight kininogen is slightly cleaved by cathepsin B into fragments of 60 kDa, and cathepsin B kininogenase activity is impaired. Our results suggest that high molecular weight kininogen is a substrate for cathepsin B under pathophysiological conditions.

Plasma prekallikrein/kallikrein processing by lysosomal cysteine proteases

Plasma kallikrein plays a role in coagulation, fibrinolysis and inflammation. Cathepsins B and L participate in (patho)physiological processes such as peptide antigen processing, tissue remodeling events, protein turnover in cells, hormone processing and tumor invasion. The present work analyzes the processing of prekallikrein/kallikrein by lysosomal cathepsins. Prekallikrein is not hydrolyzed by catB, and catL generates an inactive fragment of prekallikrein. Both kallikrein chains are hydrolyzed by catL and the light chain is mainly hydrolyzed by catB; kallikrein activity is lower after incubation with catL compared to catB. Our data suggest that the plasma kallikrein/ kinin system can be controlled by cathepsins.

Identification of prolylcarboxypeptidase as the cell matrix-associated prekallikrein activator

Investigations determined that the cell matrix-associated prekallikrein (PK) activator is prolylcarboxypeptidase. PK activation on human umbilical vein endothelial cell (HUVEC) matrix is inhibited by antipain (IC(50)=50 microM) but not anti-factor XIIa antibody, 3 mM benzamidine, 5 mM iodoacetic acid or iodoacetamide, or 3 mM N-ethylmaleimide. Corn trypsin inhibitor (IC(50)=100 nM) or Fmoc-aminoacylpyrrolidine-2-nitrile (IC(50)=100 microM) blocks matrix-associated PK activation. Angiotensin II (IC(50)=100 microM) or bradykinin (IC(50)=3 mM), but not angiotensin 1-7 or bradykinin 1-5, inhibits matrix-associated PK activation. ECV304 cell matrix PK activator also is blocked by 100 microM angiotensin II, 1 microM corn trypsin inhibitor, and 50 microM antipain, but not angiotensin 1-7. 1 mM angiotensin II or 300 microM Fmoc-aminoacylpyrrolidine-2-nitrile indirectly blocks plasminogen activation by inhibiting kallikrein formation for single chain urokinase activation. On immunoblot, prolylcarboxypeptidase antigen is associated with HUVEC matrix. These studies indicate that prolylcarboxypeptidase is the matrix PK activator.