Molecular models of the Mojave rattlesnake (Crotalus scutulatus scutulatus) venom metalloproteinases reveal a structural basis for differences in hemorrhagic activities

A Pilot STEM Curriculum Designed to Teach High School Students Concepts in Biochemical Engineering and Pharmacology

The creation of technology that affords for the design of artificial enzymes is a new branch of biochemical engineering with the objective to solve the looming global catastrophe including food shortages, energy crisis, novel diseases, climate change and environmental degradation. However, the development of science and technology that will lead to the design of artificial enzymes depends on availability of scientists with a broad range of expertise including chemistry and physics of chemical bonding, structural biochemistry of macromolecular interactions, theoretical physics and mathematics with the focus on computer modeling of dynamic docking of macromolecules. Our previous experience in university STEM education led us to conclude that in order to train future scientists with a broad expertise in STEM, it is critical for high school students to learn interdisciplinary concepts of STEM courses at an earlier age. In this article, we describe the first phase of a STEM project that involved introducing students to STEM curriculum designed to steer high school students' interest towards biochemical engineering and pharmacology. In addition, we present the outline of the STEM curriculum, along with user-friendly tutorials of AutoDock Vina, AutoDock Tools and PyMol programs that we designed to teach secondary STEM students computer modeling and docking of macromolecules. STEM high school students performed multiple exercises to understand how the potential pharmacological agents, cardiotoxins from cobra venom, interact with mitochondrial phospholipids in order to gain a deep understanding of elevated biophysical and biochemical concepts in protein drug interactions with biomembranes. We also present the results of evaluative assessments that tested students' knowledge and skills that students gained following the completion of our pilot STEM course. In brief, the assessment results showed that the students successfully acquired a high level of understanding in structural biophysics and biochemistry. Importantly, this paper provides strong proof-of-concept that our pilot STEM curriculum can be successfully integrated in the traditional American and Chinese high school classroom. The curriculum and tutorials presented in this article could be used by college and high school teachers and students in STEM classes and to support undergraduate university courses in Pharmacology, Inorganic and Organic Chemistry, Biochemistry and Structural Biology for classroom instructions and homework assignments.

Evidence for divergent patterns of local selection driving venom variation in Mojave Rattlesnakes (Crotalus scutulatus)

Snake venoms represent an enriched system for investigating the evolutionary processes that lead to complex and dynamic trophic adaptations. It has long been hypothesized that natural selection may drive geographic variation in venom composition, yet previous studies have lacked the population genetic context to examine these patterns. We leverage range-wide sampling of Mojave Rattlesnakes (Crotalus scutulatus) and use a combination of venom, morphological, phylogenetic, population genetic, and environmental data to characterize the striking dichotomy of neurotoxic (Type A) and hemorrhagic (Type B) venoms throughout the range of this species. We find that three of the four previously identified major lineages within C. scutulatus possess a combination of Type A, Type B, and a ‘mixed’ Type A + B venom phenotypes, and that fixation of the two main venom phenotypes occurs on a more fine geographic scale than previously appreciated. We also find that Type A + B individuals occur in regions of inferred introgression, and that this mixed phenotype is comparatively rare. Our results support strong directional local selection leading to fixation of alternative venom phenotypes on a fine geographic scale, and are inconsistent with balancing selection to maintain both phenotypes within a single population. Our comparisons to biotic and abiotic factors further indicate that venom phenotype correlates with fang morphology and climatic variables. We hypothesize that links to fang morphology may be indicative of co-evolution of venom and other trophic adaptations, and that climatic variables may be linked to prey distributions and/or physiology, which in turn impose selection pressures on snake venoms.

Phenotypic Variation in Mojave Rattlesnake (Crotalus scutulatus) Venom Is Driven by Four Toxin Families

Phenotypic diversity generated through altered gene expression is a primary mechanism facilitating evolutionary response in natural systems. By linking the phenotype to genotype through transcriptomics, it is possible to determine what changes are occurring at the molecular level. High phenotypic diversity has been documented in rattlesnake venom, which is under strong selection due to its role in prey acquisition and defense. Rattlesnake venom can be characterized by the presence (Type A) or absence (Type B) of a type of neurotoxic phospholipase A2 (PLA2), such as Mojave toxin, that increases venom toxicity. Mojave rattlesnakes (Crotalus scutulatus), represent this diversity as both venom types are found within this species and within a single panmictic population in the Sonoran Desert. We used comparative venom gland transcriptomics of nine specimens of C. scutulatus from this region to test whether expression differences explain diversity within and between venom types. Type A individuals expressed significantly fewer toxins than Type B individuals owing to the diversity of C-type lectins (CTLs) and snake venom metalloproteinases (SVMPs) found in Type B animals. As expected, both subunits of Mojave toxin were exclusively found in Type A individuals but we found high diversity in four additional PLA2s that was not associated with a venom type. Myotoxin a expression and toxin number variation was not associated with venom type, and myotoxin a had the highest range of expression of any toxin class. Our study represents the most comprehensive transcriptomic profile of the venom type dichotomy in rattlesnakes and C. scutulatus. Even intra-specifically, Mojave rattlesnakes showcase the diversity of snake venoms and illustrate that variation within venom types blurs the distinction of the venom dichotomy.

Insights into the Mechanisms Involved in Strong Hemorrhage and Dermonecrosis Induced by Atroxlysin-Ia, a PI-Class Snake Venom Metalloproteinase

Hemorrhage is the most prominent effect of snake venom metalloproteinases (SVMPs) in human envenomation. The capillary injury is a multifactorial effect caused by hydrolysis of the components of the basement membrane (BM). The PI and PIII classes of SVMPs are abundant in viperid venoms and hydrolyze BM components. However, hemorrhage is associated mostly with PIII-class SVMPs that contain non-catalytic domains responsible for the binding of SVMPs to BM proteins, facilitating enzyme accumulation in the tissue and enhancing its catalytic efficiency. Here we report on Atroxlysin-Ia, a PI-class SVMP that induces hemorrhagic lesions in levels comparable to those induced by Batroxrhagin (PIII-class), and a unique SVMP effect characterized by the rapid onset of dermonecrotic lesions. Atroxlysin-Ia was purified from B. atrox venom, and sequence analyses indicated that it is devoid of non-catalytic domains and unable to bind to BM proteins as collagen IV and laminin in vitro or in vivo. The presence of Atroxlysin-Ia was diffuse in mice skin, and localized mainly in the epidermis with no co-localization with BM components. Nevertheless, the skin lesions induced by Atroxlysin-Ia were comparable to those induced by Batroxrhagin, with induction of leukocyte infiltrates and hemorrhagic areas soon after toxin injection. Detachment of the epidermis was more intense in skin injected with Atroxlysin-Ia. Comparing the catalytic activity of both toxins, Batroxrhagin was more active in the hydrolysis of a peptide substrate while Atroxlysin-Ia hydrolyzed more efficiently fibrin, laminin, collagen IV and nidogen. Thus, the results suggest that Atroxlysin-Ia bypasses the binding step to BM proteins, essential for hemorrhagic lesions induced by PII- and P-III class SVMPs, causing a significantly fast onset of hemorrhage and dermonecrosis, due to its higher proteolytic capacity on BM components.

The Compartment Syndrome Associated with Deep Vein Thrombosis due to Rattlesnake Bite: A Case Report

Background:

Snakebite is a health issue specific to some parts of the world, especially in the tropical areas, where it produces many victims. The main clinical damage caused by snakebite involves haemotoxic, neurotoxic and myotoxic reactions. We report the case of a young woman suffering from snakebite who developed deep vein thrombosis and compartment syndrome.

Case Report:

We present the case of a 32-year-old Romanian woman who was injured by her own Crotalinae snake (also known as pit viper or rattlesnake) on her left forearm. When admitted to our Emergency Department, she was conscious with a Glasgow coma scale of 12/15, somnolent, febrile, suffering of headache, tachypnoea; the marks of the snakebite were located in the distal part of the anterior left forearm; she had pain and bleeding at the bite site and swelling of the left upper limb with lymphangitis up to the axilla. She experienced fasciotomy-requiring compartment syndrome of the upper limb and required unfractionated heparin and close monitoring using activated partial thromboplastin time evolution due to micro-thrombosis in the brachial vein. Local improvement was achieved in the next 4 days with progressive diminishment of local tenderness and swelling.

Conclusion:

Limb deep vein thrombosis might be induced by snakebite, despite the pro-haemorrhagic general condition induced by the envenomation. A high index of clinical suspicion is needed for early diagnosis and timely management, which can improve survival of these patients.

The Possible Role of Nonbilayer Structures in Regulating ATP Synthase Activity in Mitochondrial Membranes

The effects of temperature and of the membrane-active protein CTII on the formation of nonbilayer structures in mitochondrial membranes were studied by 31P-NMR. Increasing the temperature of isolated mitochondrial fractions correlated with an increase in ATP synthase activity and the formation of nonbilayer packed phospholipids with immobilized molecular mobility. Computer modeling was employed for analyzing the interaction of mitochondrial membrane phospholipids with the molecular surface of CTII, which behaves like a dicyclohexylcarbodiimide-binding protein (DCCD-BP) of the F0 group in a lipid phase. Overall, our studies suggest that proton permeability toroidal pores formed in mitochondrial membranes consist of immobilized nonbilayer-packed phospholipids formed via interactions with DCCD-BP. Our studies support the existence of a proton transport along a concentration gradient mediated via transit toroidal permeability pores which induce conformational changes necessary for mediating the catalytic activity of ATP synthase in the subunits of the F0-F1 complex.

COMPARATIVE ANALYSIS OF BIOLOGICAL AND BIOCHEMICAL VENOM CHARACTERISTICS OF NORTH AND SOUTH AMERICAN Crotalus (SERPENTES: VIPERIDAE) SNAKE SPECIES: AN INTRODUCTORY APPROXIMATION TO UNDERSTAND THEIR BIOLOGICAL FUNCTIONS

In this study, venom samples of rattlesnakes from the United States of America and Venezuela Bolivarian Republic were tested for their gelatinase, fibrinolytic, hemorrhagic and coagulant activities, as well as inhibition of platelet function. Electrophoretic titration curves on polyacrylamide gel were used to compare protein composition. There were different protease activities in the venoms. Hemorrhagic activity showed high geographic variation, but northern specimens had a higher trend in this parameter. Differences in venom protein conformation were palpable between snakes from the North and South America. There was a distinct protein composition among all venoms, several venoms presented hemorrhagic and fibrinolytic activities, and different performance on platelet assays. These results demonstrate the interesting differences between North and South America Crotalus venoms.

Unraveling the distinctive features of hemorrhagic and non-hemorrhagic snake venom metalloproteinases using molecular simulations

Snake venom metalloproteinases are important toxins that play fundamental roles during envenomation. They share a structurally similar catalytic domain, but with diverse hemorrhagic capabilities. To understand the structural basis for this difference, we build and compare two dynamical models, one for the hemorrhagic atroxlysin-I from Bothrops atrox and the other for the non-hemorraghic leucurolysin-a from Bothrops leucurus. The analysis of the extended molecular dynamics simulations shows some changes in the local structure, flexibility and surface determinants that can contribute to explain the different hemorrhagic activity of the two enzymes. In agreement with previous results, the long Ω-loop (from residue 149 to 177) has a larger mobility in the hemorrhagic protein. In addition, we find some potentially-relevant differences at the base of the S1' pocket, what may be interesting for the structure-based design of new anti-venom agents. However, the sharpest differences in the computational models of atroxlysin-I and leucurolysin-a are observed in the surface electrostatic potential around the active site region, suggesting thus that the hemorrhagic versus non-hemorrhagic activity is probably determined by protein surface determinants.

Snake Venom Cytotoxins, Phospholipase A2s, and Zn2+-dependent Metalloproteinases: Mechanisms of Action and Pharmacological Relevance

Snake venom toxins are responsible for causing severe pathology and toxicity following envenomation including necrosis, apoptosis, neurotoxicity, myotoxicity, cardiotoxicity, profuse hemorrhage, and disruption of blood homeostasis. Clinically, snake venom toxins therefore represent a significant hazard to snakebite victims which underscores the need to produce more efficient anti-venom. Some snake venom toxins, however, have great potential as drugs for treating human diseases. In this review, we discuss the biochemistry, structure/function, and pathology induced by snake venom toxins on human tissue. We provide a broad overview of cobra venom cytotoxins, catalytically active and inactive phospholipase A2s (PLA2s), and Zn2+-dependent metalloproteinases. We also propose biomedical applications whereby snake venom toxins can be employed for treating human diseases. Cobra venom cytotoxins, for example, may be utilized as anti-cancer agents since they are efficient at destroying certain types of cancer cells including leukemia. Additionally, increasing our understanding of the molecular mechanism(s) by which snake venom PLA2s promote hydrolysis of cell membrane phospholipids can give insight into the underlying biomedical implications for treating autoimmune disorders that are caused by dysregulated endogenous PLA2 activity. Lastly, we provide an exhaustive overview of snake venom Zn2+-dependent metalloproteinases and suggest ways by which these enzymes can be engineered for treating deep vein thrombosis and neurodegenerative disorders.