Understanding structural and functional aspects of PII snake venom metalloproteinases: Characterization of BlatH1, a hemorrhagic dimeric enzyme from the venom of Bothriechis lateralis

Gene expression of secretory proteins in the nuptial pads of three Lithobates species (Anura: Ranidae)

Many amphibian species possess male-specific secretory breeding glands. In anurans, such specialized glands are often present as nuptial pads at the first digit of the hand, which are pressed against the female during amplexus. However, the role of nuptial pad secretions remains largely unknown. Here, we investigate the inner morphology as well as the RNA expression patterns of the nuptial pads of several Central American Lithobates species (Ranidae). As shown for the breeding glands of other amphibian species, the Lithobates nuptial pads are composed of large specialized mucus glands, excreting proteinaceous content to the surface. Whole-transcriptome sequencing revealed that for one of the species the most highly expressed transcripts encoding secretory proteins in the nuptial pads are sodefrin precursor-like factor (SPF) proteins, known to have a pheromone function in multiple amphibian species. The other two species, however, lack high expression of SPF transcripts but express other secretory proteins, whose roles in amphibian breeding glands remain unknown. Several of these proteins are highly expressed in all samples, suggesting a direct role during courtship or for the maintenance/development of the glands.

"Computational and Functional Characterization of a Hemorrhagic Metalloproteinase Purified from Cerastes cerastes Venom"

Structural and functional aspects of snake venoms metalloproteinases (SVMPs) have been extensively studied due to their role in envenomation. However, in the detection of certain coagulation disorders these biomolecules have been used and applied for the production of new thrombolytic drugs. CcMP-II, a SVMP-II metalloproteinase with a hemorrhagic activity, isolated from the venom of Cerastes cerastes, its sequence of 472 amino acids was identified. Predicted 3D structure showed an arrangement of CcMP-II into two distinct domains: i) a metalloproteinase domain where the zinc-binding motif is found (HXXGHNLGIDH) in addition to the sequence Cys-Ile-Met (CIM) at the Met-turn and ii) disintegrin-like domain containing RGD motif. CcMP-II inhibits platelet aggregation induced by collagen in a dose-dependent manner with an IC₅₀ value estimated of 0.11 nM. This proteinase inhibits also aggregation of platelet stimulated by collagen even if the metal chelating agents (EDTA and 1, 10-phenontroline) are present suggesting that anti-aggregating effect is not due to its metalloproteinase domain, but to its disintegrin-like domain. Capillary pathological modifications caused by CcMP-II following intramuscular injection have as well been examined in mice. The key morphological alterations of the capillary vessels were clearly apparent from the ultrastructural study. The CcMP-II can play a key function in the pathogenesis of disorders that occurs following envenomation of Cerastes cerastes. The three-dimensional model of CcMP-II was built to explain structure-function relationships in ADAM/ADAMTs, a family of proteins having significant therapeutic potential. In order to explain structure-function relationships in ADAM / ADAMT, a family of proteins with considerable therapeutic potential, the three-dimensional model of CcMP-II was constructed.

Basement membrane degradation and inflammation play a role in the pulmonary hemorrhage induced by a P-III snake venom metalloproteinase

Snakebite envenoming is a neglected tropical disease affecting millions of people every year, especially in vulnerable rural populations in the developing world. Viperid snakes cause envenomings characterized by a complex pathophysiology which includes local and systemic hemorrhage due to the action of snake venom metalloproteinases (SVMPs). The pathogenesis of SVMP-induced systemic hemorrhage has not been investigated in detail. This study explored the pulmonary hemorrhage induced in a murine model by a P-III SVMP from the venom of Crotalus simus. Histological analysis revealed extravasation in the lungs as early as 15 min after intravenous injection of the toxin, and hemorrhage increased at 360 min. Western blot analysis demonstrated the cleavage of basement membrane (BM) proteins in lung homogenates and in bronchoalveolar lavage fluid, implying an enzymatic disruption of this extracellular matrix structure at the capillary-alveolar barrier. Likewise, alveolar edema was observed, with an increment in protein concentration in the bronchoalveolar lavage fluid, and a neutrophil-rich inflammatory infiltrate was present in the parenchyma of the lungs as part of the inflammatory reaction. Pretreatment of mice with indomethacin, pentoxifylline and an anti-neutrophil antibody resulted in a significant decrease in pulmonary hemorrhage at 360 min. These findings suggest that this P-III SVMP induces acute lung injury through the direct action of this enzyme in the capillary-alveolar barrier integrity, as revealed by BM degradation, and as a consequence of the inflammatory reaction that develops in lung tissue. Our findings provide novel clues to understand the mechanism of action of hemorrhagic SVMPs in the lungs.

Snake Venom Metalloproteinases (SVMPs): A structure-function update

Snake venom metalloproteinases (SVMPs) represent a diverse group of multi-domain proteins with several biological activities such as the ability to induce hemorrhage, proteolytic degradation of fibrinogen and fibrin, induction of apoptosis and inhibition of platelet aggregation. Due to these activities, SVMPs are responsible for many of the well-known pathological phenotypes in snake envenomations caused particularly by species from the Viperidae family and the Crotalinae subfamily. These proteins have been classified based on their size and domain structure into P–I, P-II and P-III classes. Comparatively, members of the P–I SVMPs possess the simplest structures, formed by the catalytic metalloproteinase domain only; the P-II SVMPs are moderately more complex, having the canonical disintegrin domain in addition to the metalloproteinase domain; members of the P-III class are more structurally varied, comprising the metalloproteinase, disintegrin-like, and cysteine-rich domains. Proteolytic cleavage, repeated domain loss and presence of other ancillary domains are responsible for structural diversities in the P-III class. However, studies continue to unveil the relationship between the structure and function of these proteins. In this review, we recovered evidences from literature on the structural peculiarities and functional classification of Snake Venom Metalloproteinases. In addition, we reflect on diversities that exist among each class while taking into account specific and up-to-date class-based activities.

Boyer L, D. Possani L, López-Casillas F, Olvera A, Romero C, Zamudio F, Alagón A. Neotropical Rattlesnake (Crotalus simus) Venom Pharmacokinetics in Lymph and Blood Using an Ovine Model

The most abundant protein families in viper venoms are Snake Venom Metalloproteases (SVMPs), Snake Venom Serine Proteases (SVSPs) and Phospholipases (PLA₂s). These are primarily responsible for the pathophysiology caused by the bite of pit-vipers; however, there are few studies that analyze the pharmacokinetics (PK) of whole venom (WV) and its protein families. We studied the pathophysiology, PK profile and differential absorption of representative toxins from venom of Neotropical Rattlesnake (Crotalus simus) in a large animal model (ovine). Toxins studied included crotoxin (the main lethal component), which causes moderate to severe neurotoxicity; SVSPs, which deplete fibrinogen; and SVMPs, which cause local tissue damage and local and systemic hemorrhage. We found that Whole Venom (WV) was highly bioavailable (86%) 60 h following intramuscular (IM) injection, and extrapolation suggests that bioavailability may be as high as 92%. PK profiles of individual toxins were consistent with their physicochemical properties and expected clinical effects. Lymph cannulated animals absorbed 1.9% of WV through lymph during the first 12 h. Crotoxin was minimally detectable in serum after intravenous (IV) injection; however, following IM injection it was detected in lymph but not in blood. This suggests that crotoxin is quickly released from the blood toward its tissue targets.

The role of platelets in hemostasis and the effects of snake venom toxins on platelet function

The human body has a set of physiological processes, known as hemostasis, which keeps the blood fluid and free of clots in normal vessels; in the case of vascular injury, this process induces the local formation of a hemostatic plug, preventing hemorrhage. The hemostatic system in humans presents complex physiological interactions that involve platelets, plasma proteins, endothelial and subendothelial structures. Disequilibrium in the regulatory mechanisms that control the growth and the size of the thrombus is one of the factors that favors the development of diseases related to vascular disorders such as myocardial infarction and stroke, which are among the leading causes of death in the western world. Interfering with platelet function is a strategy for the treatment of thrombotic diseases. Antiplatelet drugs are used mainly in cases related to arterial thrombosis and interfere in the formation of the platelet plug by different mechanisms. Aspirin (acetylsalicylic acid) is the oldest and most widely used antithrombotic drug. Although highly effective in most cases, aspirin has limitations compared to other drugs used in the treatment of homeostatic disorders. For this reason, research related to molecules that interfere with platelet aggregation are of great relevance. In this regard, snake venoms are known to contain a number of molecules that interfere with hemostasis, including platelet function. The mechanisms by which snake venom components inhibit or activate platelet aggregation are varied and can be used as tools for the diagnosis and the treatment of several hemostatic disorders. The aim of this review is to present the role of platelets in hemostasis and the mechanisms by which snake venom toxins interfere with platelet function.

Wasp venomic: Unravelling the toxins arsenal of Polybia paulista venom and its potential pharmaceutical applications

Polybia paulista (Hymenoptera: Vespidae) is a neotropical social wasp from southeast Brazil. As most social Hymenoptera, venom from P. paulista comprises a complex mixture of bioactive toxins ranging from low molecular weight compounds to peptides and proteins. Several efforts have been made to elucidate the molecular composition of the P. paulista venom. Data derived from proteomic, peptidomic and allergomic analyses has enhanced our understanding of the whole envenoming process caused by the insect sting. The combined use of bioinformatics, -omics- and molecular biology tools have allowed the identification, characterization, in vitro synthesis and recombinant expression of several wasp venom toxins. Some of these P. paulista - derived bioactive compounds have been evaluated for the rational design of antivenoms and the improvement of allergy specific diagnosis and immunotherapy. Molecular characterization of crude venom extract has enabled the description and isolation of novel toxins with potential biotechnological applications. Here, we review the different approaches that have been used to unravel the venom composition of P. paulista. We also describe the main groups of P. paulista - venom toxins currently identified and analyze their potential in the development of component-resolved diagnosis of allergy, and in the rational design of antivenoms and novel bioactive drugs.

Novel Catalytically-Inactive PII Metalloproteinases from a Viperid Snake Venom with Substitutions in the Canonical Zinc-Binding Motif

Snake venom metalloproteinases (SVMPs) play key biological roles in prey immobilization and digestion. The majority of these activities depend on the hydrolysis of relevant protein substrates in the tissues. Hereby, we describe several isoforms and a cDNA clone sequence, corresponding to PII SVMP homologues from the venom of the Central American pit viper Bothriechis lateralis, which have modifications in the residues of the canonical sequence of the zinc-binding motif HEXXHXXGXXH. As a consequence, the proteolytic activity of the isolated proteins was undetectable when tested on azocasein and gelatin. These PII isoforms comprise metalloproteinase and disintegrin domains in the mature protein, thus belonging to the subclass PIIb of SVMPs. PII SVMP homologues were devoid of hemorrhagic and in vitro coagulant activities, effects attributed to the enzymatic activity of SVMPs, but induced a mild edema. One of the isoforms presents the characteristic RGD sequence in the disintegrin domain and inhibits ADP- and collagen-induced platelet aggregation. Catalytically-inactive SVMP homologues may have been hitherto missed in the characterization of snake venoms. The presence of such enzymatically-inactive homologues in snake venoms and their possible toxic and adaptive roles deserve further investigation.

Processing of Snake Venom Metalloproteinases: Generation of Toxin Diversity and Enzyme Inactivation

Snake venom metalloproteinases (SVMPs) are abundant in the venoms of vipers and rattlesnakes, playing important roles for the snake adaptation to different environments, and are related to most of the pathological effects of these venoms in human victims. The effectiveness of SVMPs is greatly due to their functional diversity, targeting important physiological proteins or receptors in different tissues and in the coagulation system. Functional diversity is often related to the genetic diversification of the snake venom. In this review, we discuss some published evidence that posit that processing and post-translational modifications are great contributors for the generation of functional diversity and for maintaining latency or inactivation of enzymes belonging to this relevant family of venom toxins.

Hemorrhage Caused by Snake Venom Metalloproteinases: A Journey of Discovery and Understanding

The historical development of discoveries and conceptual frames for understanding the hemorrhagic activity induced by viperid snake venoms and by hemorrhagic metalloproteinases (SVMPs) present in these venoms is reviewed. Histological and ultrastructural tools allowed the identification of the capillary network as the main site of action of SVMPs. After years of debate, biochemical developments demonstrated that all hemorrhagic toxins in viperid venoms are zinc-dependent metalloproteinases. Hemorrhagic SVMPs act by initially hydrolyzing key substrates at the basement membrane (BM) of capillaries. This degradation results in the weakening of the mechanical stability of the capillary wall, which becomes distended owing of the action of the hemodynamic biophysical forces operating in the circulation. As a consequence, the capillary wall is disrupted and extravasation occurs. SVMPs do not induce rapid toxicity to endothelial cells, and the pathological effects described in these cells in vivo result from the mechanical action of these hemodynamic forces. Experimental evidence suggests that degradation of type IV collagen, and perhaps also perlecan, is the key event in the onset of microvessel damage. It is necessary to study this phenomenon from a holistic, systemic perspective in which the action of other venom components is also taken into consideration.

Tissue localization and extracellular matrix degradation by PI, PII and PIII snake venom metalloproteinases: clues on the mechanisms of venom-induced hemorrhage

Snake venom hemorrhagic metalloproteinases (SVMPs) of the PI, PII and PIII classes were compared in terms of tissue localization and their ability to hydrolyze basement membrane components in vivo, as well as by a proteomics analysis of exudates collected in tissue injected with these enzymes. Immunohistochemical analyses of co-localization of these SVMPs with type IV collagen revealed that PII and PIII enzymes co-localized with type IV collagen in capillaries, arterioles and post-capillary venules to a higher extent than PI SVMP, which showed a more widespread distribution in the tissue. The patterns of hydrolysis by these three SVMPs of laminin, type VI collagen and nidogen in vivo greatly differ, whereas the three enzymes showed a similar pattern of degradation of type IV collagen, supporting the concept that hydrolysis of this component is critical for the destabilization of microvessel structure leading to hemorrhage. Proteomic analysis of wound exudate revealed similarities and differences between the action of the three SVMPs. Higher extent of proteolysis was observed for the PI enzyme regarding several extracellular matrix components and fibrinogen, whereas exudates from mice injected with PII and PIII SVMPs had higher amounts of some intracellular proteins. Our results provide novel clues for understanding the mechanisms by which SVMPs induce damage to the microvasculature and generate hemorrhage.

Local and systemic hemorrhage are typical manifestations of envenomings by viperid snakes. Hemorrhagic activity is due to the action of snake venom metalloproteinases (SVMPs) in the microvasculature, especially in capillaries. There are large differences in the hemorrhagic potential of SVMPs, depending on their domain composition. The present study compared PI, PII and PIII hemorrhagic SVMPs for their tissue distribution and their ability to cleave proteins of the extracellular matrix (ECM), especially those of the basement membrane (BM) that provides mechanical stability to microvessels. Observations indicate that PII and PIII SVMPs, which exert a high hemorrhagic activity, are preferentially located in microvessels, whereas PI SVMP is distributed in a more widespread fashion in the tissue. In addition, when these toxins are injected at doses that induce a similar hemorrhagic effect, they cleave type IV collagen to a similar extent, showing differences in the cleavage patterns of other ECM components, such as laminin, nidogen and type VI collagen. The analysis of the exudates resultant from the action of these SVMPs in the tissue revealed many similarities and some differences in the exudate proteomes. Overall our results indicate that hydrolysis of type IV collagen is a key event in the onset of microvessel damage, and that the ability of SVMPs to bind to microvessels greatly determines their hemorrhagic potential.