The predatory ecology of Varanus komodoensis (Komodo Dragon) has been a subject of long-standing interest and considerable conjecture. Here, we investigate the roles and potential interplay between cranial mechanics, toxic bacteria, and venom. Our analyses point to the presence of a sophisticated combined-arsenal killing apparatus. We find that the lightweight skull is relatively poorly adapted to generate high bite forces but better adapted to resist high pulling loads. We reject the popular notion regarding toxic bacteria utilization. Instead, we demonstrate that the effects of deep wounds inflicted are potentiated through venom with toxic activities including anticoagulation and shock induction. Anatomical comparisons of V. komodoensis with V. (Megalania) priscus fossils suggest that the closely related extinct giant was the largest venomous animal to have ever lived. evolution ͉ phylogeny ͉ squamate ͉ protein ͉ toxin P redation by Varanus komodoensis, the world's largest extant lizard, has been an area of great controversy (cf. ref. 1). Three-dimensional finite element (FE) modeling has suggested that the skull and bite force of V. komodoensis are weak (2). However, the relevance of bite force and cranial mechanics to interpretations of feeding behavior cannot be fully evaluated in the absence of comparative data. Moreover, this previous analysis did not account for gape angle, which can significantly influence results (3). Irrespective of evidence for or against a powerful bite, V. komodoensis is clearly capable of opening wounds that can lead to death through blood loss (4). Controversially, the proposition that utilization of pathogenic bacteria facilitates the prey capture (4, 5) has been widely accepted despite a conspicuous lack of supporting evidence for a role in predation. In contrast, recent evidence has revealed that venom is a basal characteristic of the Toxicofera reptile clade (6), which includes the varanid lizards (7), suggesting a potential role of venom in prey capture by V. komodoensis that has remained unexplored. This is consistent with prey animals reported as being unusually quiet after being bitten and rapidly going into shock (4) and the anecdotal reports of persistent bleeding in human victims after bites (including B.G.F.'s personal observations). Shock-inducing and prolonged bleeding pathophysiological effects are also characteristic of helodermatid lizard envenomations (cf. ref . 8), consistent with the similarity between helodermatid and varanid venoms (6).Here, we examine the feeding ecology of V. komodoensis in detail. We compare the skull architecture and dentition with the related extinct giant V. priscus (Megalania). In this 3D finite element modeling of reptilian cranial mechanics that applies a comparative approach, we also compare the bite force and skull stress performance with that of Crocodylus porosus (Australian Saltwater Crocodile), including the identification of optimal gape angle (an aspect not considered in previous nonreptilian comparative FE analyses). We als...

The origin and evolution of venom proteins in helodermatid lizards were investigated by multidisciplinary techniques. Our analyses elucidated novel toxin types resultant from three unique domain-expression processes: 1) The first full-length sequences of lethal toxin isoforms (helofensins) revealed this toxin type to be constructed by an ancestral monodomain, monoproduct gene (beta-defensin) that underwent three tandem domain duplications to encode a tetradomain, monoproduct with a possible novel protein fold; 2) an ancestral monodomain gene (encoding a natriuretic peptide) was medially extended to become a pentadomain, pentaproduct through the additional encoding of four tandemly repeated proline-rich peptides (helokinestatins), with the five discrete peptides liberated from each other by posttranslational proteolysis; and 3) an ancestral multidomain, multiproduct gene belonging to the vasoactive intestinal peptide (VIP)/glucagon family being mutated to encode for a monodomain, monoproduct (exendins) followed by duplication and diversification into two variant classes (exendins 1 and 2 and exendins 3 and 4). Bioactivity characterization of exendin and helokinestatin elucidated variable cardioactivity between isoforms within each class. These results highlight the importance of utilizing evolutionary-based search strategies for biodiscovery and the virtually unexplored potential of lizard venoms in drug design and discovery.

Because of significant differences in anatomy of the venom delivery system and distant phylogenetic relatedness, it had been long assumed that the venom systems of snakes and helodermatid lizards were independently evolved (1-3). However, both lineages were recently revealed to be members of a clade (Toxicofera) that also included several lineages of other lizards recently shown to be venomous (4, 5). In contrast to the hypothesis of independent origins, this new perspective revealed that lizard and snake venom systems are homologous but highly differentiated descendants of an early evolved venom system in squamates. The basal condition was incipient glands on both the mandibular and maxillary regions with snakes favoring the maxillary venom glands and secondarily losing the mandibular venom glands. However, the anguimorph lizards (anguids, helodermatids, and varanids) did the reverse, resulting in the modern condition seen today.The lizard venom delivery system is less sophisticated than the high pressure injection mechanism of the front fanged advanced snakes, and the vast majority of the species pose trivial direct medical risks to human (with the exception of helodermatids and large varanids such as Varanus komodoensis). However, the effects of envenomation from mediFrom the

The lethal factor in stonefish venom is stonustoxin (SNTX), a heterodimeric cytolytic protein that induces cardiovascular collapse in humans and native predators. Here, using X-ray crystallography, we make the unexpected finding that SNTX is a pore-forming member of an ancient branch of the Membrane Attack ComplexPerforin/Cholesterol-Dependent Cytolysin (MACPF/CDC) superfamily. SNTX comprises two homologous subunits (α and β), each of which comprises an N-terminal pore-forming MACPF/CDC domain, a central focal adhesion-targeting domain, a thioredoxin domain, and a C-terminal tripartite motif family-like PRY SPla and the RYanodine Receptor immune recognition domain. Crucially, the structure reveals that the two MACPF domains are in complex with one another and arranged into a stable early prepore-like assembly. These data provide long sought after near-atomic resolution insights into how MACPF/CDC proteins assemble into prepores on the surface of membranes. Furthermore, our analyses reveal that SNTX-like MACPF/CDCs are distributed throughout eukaryotic life and play a broader, possibly immune-related function outside venom.H uman envenoming by the tropical stonefish (Synanceia horrida and related species) results in extreme pain, edema, hypotension, respiratory distress, and on rare occasions, death (1). The lethal factor in stonefish venom is an ∼150-kDa protein termed stonustoxin (SNTX), an unusual example of a vertebrate cytolytic protein complex (2). SNTX is a soluble heterodimeric assembly of two closely related proteins termed SNTX-α and -β that share sequence identity of ∼50% (3). With the exception of a C-terminal PRY SPla and the RYanodine Receptor (PRYSPRY) domain in each protein (4), SNTX shares no obvious sequence similarity to any structurally or functionally characterized molecule. SNTX induces species-specific hemolytic activity (2) by an apparent pore-forming mechanism (5). It induces platelet aggregation (6), and like the closely related Trachynilysin (from Synanceia trachynis), SNTX exhibits activity suggesting that it may function as a neurotoxin (7,8).Because eukaryote pore-forming toxins are relatively rare, we reasoned that SNTX might represent a new exemplar of a vertebrate pore-forming protein. Previous studies had shown that it was possible to purify and crystallize SNTX (9); however, no structure has been reported to date. Accordingly, to address the structural basis for SNTX activity, we determined its X-ray crystal structure.