Characterization of three hemorrhagic factors from the venom of Okinawa habu (Trimeresurus flavoviridis)

The Protobothrops flavoviridis Hemorrhagic Metalloproteinase HR2 Is Inhibited by Human Alpha 2-Macroglobulin

Vaccinations with habu (Protobothrops flavoviridis) venom toxoid were administered to individuals living in Amami Oshima from 1965 to 2002, and its effectiveness was investigated in 1991. The results raised the possibility that normal human serum inherently contains an inhibitor of the hemorrhagic metalloproteinase HR2, considered to be one of the major components of habu venom. In this study, we investigated the interaction between the hemorrhagic metalloproteinases HR1 and HR2 from habu-venom and human alpha 2-macroglobulin (α2M). Hemorrhagic activity of HR2 was completely inhibited by human α2M. However, the hemorrhagic activity of the large molecule HR1a was not inhibited. Size exclusion chromatography revealed that human α2M captured the HR2 molecule and formed a complex with it, thus inhibiting hemorrhagic activity. These results suggest that human α2M plays an important role in the inhibition of hemorrhage induced by HR2 from habu venom.

Snake venoms are integrated systems, but abundant venom proteins evolve more rapidly

Background

While many studies have shown that extracellular proteins evolve rapidly, how selection acts on them remains poorly understood. We used snake venoms to understand the interaction between ecology, expression level, and evolutionary rate in secreted protein systems. Venomous snakes employ well-integrated systems of proteins and organic constituents to immobilize prey. Venoms are generally optimized to subdue preferred prey more effectively than non-prey, and many venom protein families manifest positive selection and rapid gene family diversification. Although previous studies have illuminated how individual venom protein families evolve, how selection acts on venoms as integrated systems, is unknown.

Results

Using next-generation transcriptome sequencing and mass spectrometry, we examined microevolution in two pitvipers, allopatrically separated for at least 1.6 million years, and their hybrids. Transcriptomes of parental species had generally similar compositions in regard to protein families, but for a given protein family, the homologs present and concentrations thereof sometimes differed dramatically. For instance, a phospholipase A₂ transcript comprising 73.4 % of the Protobothrops elegans transcriptome, was barely present in the P. flavoviridis transcriptome (<0.05 %). Hybrids produced most proteins found in both parental venoms. Protein evolutionary rates were positively correlated with transcriptomic and proteomic abundances, and the most abundant proteins showed positive selection. This pattern holds with the addition of four other published crotaline transcriptomes, from two more genera, and also for the recently published king cobra genome, suggesting that rapid evolution of abundant proteins may be generally true for snake venoms. Looking more broadly at Protobothrops, we show that rapid evolution of the most abundant components is due to positive selection, suggesting an interplay between abundance and adaptation.

Conclusions

Given log-scale differences in toxin abundance, which are likely correlated with biosynthetic costs, we hypothesize that as a result of natural selection, snakes optimize return on energetic investment by producing more of venom proteins that increase their fitness. Natural selection then acts on the additive genetic variance of these components, in proportion to their contributions to overall fitness. Adaptive evolution of venoms may occur most rapidly through changes in expression levels that alter fitness contributions, and thus the strength of selection acting on specific secretome components.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1832-6) contains supplementary material, which is available to authorized users.

The occurrence of HR1b in the venom of the snake Okinawa habu (Protobothrops flavoviridis)

This study describes the first isolation of hemorrhagic metalloproteinase HR1b from the venom of Okinawa habu, and its cDNA cloning. The substrate specificity of isolated HR1b definitely differed from that of HR1a, further supporting the presence of a metalloproteinase distinguishable from HR1a in the venom of Okinawa habu. The deduced amino acid sequence of HR1b showed 99.67% identity with HR1b of Amami habu, with only two amino acid residue replacements.

Neutralization of hemorrhagic snake venom metalloproteinase HR1a from Protobothrops flavoviridis by human monoclonal antibody

Human monoclonal antibodies (HuMAbs) against HR1a from Protobothrops (formerly Trimeresurus) flavoviridis venom were obtained by the fusion of SP2/0-Ag14 myeloma cells and spleen cells from KM mice immunized with purified HR1a. The ability of HuMAbs to neutralize the HR1a was determined by in vitro neutralization assay and by neutralization of the hemorrhagic activity. The initial screening of over 300 hybridoma fusion wells resulted in the establishment of 80 HR1a-reactive hybridomas. Of the reactive clones, HuMAb HR1a-7 and HR1a-18 neutralized both proteolytic and hemorrhagic activity of HR1a. Mapping of epitope recognized by the reactive clones was performed by using an ELISA that measured antibody binding to overlapping peptides (15 amino acid peptide offset frameshifted by three residues) covering the metalloproteinase domain sequence of HR1a. HuMAbs HR1a-7 and HR1a-18 neutralized HR1a by reacting with peptides of EQQRYLNNFRFIELV and IVNTLNETYRYL. The three-dimensional structure of HR1a based on a homology modeling predicted that these two epitopes are surface exposed.

Intraarticular envenomation by Trimeresurus flavomaculatus mcgregori resulting in joint destruction

This article reports a case of digital intraarticular envenomation from a T. flavomaculatus mcgregori pit viper resulting in severe joint damage. Bites by these snakes are rare in the U.S.A. since this species is only found in collections and zoos. Intraarticular envenomations from crotalids are rare and may result in joint destruction.

Characterization of a hemorrhagic factor, LHF-I, isolated from the bushmaster snake (Lachesis muta muta) venom

Hemorrhagic factor I (LHF-I) was previously purified from the venom of the bushmaster snake (Lachesis muta muta). In terms of biochemical and immunological properties, LHF-I is a glycoprotein (mol. wt 100,000, pI 4.7) consisting of two subunits; it loses its activity following mercaptoethanol treatment. LHF-I contains 0.7 g-atom zinc and 1.2 g-atom calcium per mole protein. The hemorrhagic and the proteinase activities are inhibited by EDTA; subsequent addition of Ca2+ or Mg2+ does not reverse the EDTA-induced inhibition of the hemorrhagic activity. The metalloenzyme does not hyrolyze arginine esters and is devoid of phospholipase A2 activity. It hydrolyzes the A alpha- > B beta-chain of fibrinogen without clot formation and hydrolyzes selectively the alpha-chain of fibrin, leaving the B beta- and tau-chains unaffected. Antibodies to the hemorrhagic factor in bushmaster venom were produced by immunizing rabbits with the purified protein. The antibody was purified by protein-A affinity chromatography. This antibody was also used to screen other Crotalinae venom samples for immunologically similar epitopes by ELISA assay. The purified antibody reacted only with LHF-I and two samples of bushmaster venom from different geographical locations.

The primary structure of a hemorrhagic factor, HR2b, from the venom of Okinawa habu (Trimeresurus flavoviridis)

The complete amino acid sequence of a hemorrhagic factor, HR2b, from the venom of Okinawa habu was determined. The hemorrhagic factor was fragmented by CNBr cleavage, trypsin, staphylococcal protease V8 and lysyl endopeptidase digestions. The resulting peptides were purified on high performance chromatography, and sequenced by Edman degradation. HR2b was composed of 204 amino acids with pyroglutamyl residue at the amino terminus, and the calculated mol. wt based on the amino acid composition was 23,335. There are three disulfide linkages in the primary structure. The consensus sequence (His-Glu-Xaa-Xaa-His) for zinc-binding site of zinc-requiring metalloproteinases was found in the structure. The primary structure of HR2b shows a significant similarity with that of HR2a of Amami habu venom; 98.5% identity.

Hemorrhagic metalloproteinases from snake venoms

One of the more significant consequences of crotalid envenomation is hemorrhage. Over the past 50 years of investigation, it is clear that the primary factors responsible for hemorrhage are metalloproteinases present in the venom of these snakes. The biochemical basis for their activity is the proteolytic destruction of basement membrane and extracellular matrix surrounding capillaries and small vessels. These proteinase toxins may also interfere with coagulation, thus complementing loss of blood from the vasculature. Structural studies have shown that these proteinases are synthesized as zymogens and are processed at both the amino and carboxy termini to give the mature protein. The variety of hemorrhagic toxins found in snake venoms is due to the presence of structurally related proteins composed of various domains. The type of domains found in each toxin plays an important role in the hemorrhagic potency of the protein. Recently, structural homologs to the venom hemorrhagic metalloproteinases have been identified in several mammalian reproductive systems. The functional significance of the reproductive proteins is not clear, but in light of the presence of similar domains shared with the venom metalloproteinases, their basic biochemical activities may be similar but with very different consequences. This review discusses the history of hemorrhagic toxin research with emphasis on the Crotalus atrox proteinases. The structural similarities observed among the hemorrhagic toxins are outlined, and the structural relationships of the toxins to the mammalian reproductive proteins are described.

Isolation and characterization of a hemorrhagin from the venom of Calloselasma rhodostoma (Malayan pit viper)

The major hemorrhagin (termed rhodostoxin) of the venom of Calloselasma rhodostoma (Malayan pit viper) was purified to electrophoretic homogeneity by Sephadex G-200 gel filtration followed by high performance ion exchange chromatography. The purified hemorrhagin also yielded a single peak in reversed-phase HPLC. It had an isoelectric point of 5.3 and a mol. wt of 34,000. Rhodostoxin exhibited potent proteolytic, hemorrhagic and edema-inducing activities but was not lethal to mice at a dose of 6 microgram/g (i.v.). Treatment of rhodostoxin with EDTA eliminated both the proteolytic and hemorrhagic activities completely. The N-terminal sequence of rhodostoxin was determined to be NHEIKRHVDIVVVXDSRFCTK.

Structural domains in venom proteins: evidence that metalloproteinases and nonenzymatic platelet aggregation inhibitors (disintegrins) from snake venoms are derived by proteolysis from a common precursor

A comparison of the structures of a precursor of trigramin (a disintegrin), metalloproteinases, disintegrins and related proteins, suggests the existence of common precursors for metalloproteinases and disintegrins. The proposed common precursor and related proteins have four distinct domains (A-D). Domain B contains the metal binding site and the catalytic Glu residue, which comprise the active site of metalloproteinases. Domain C contains the Arg-Gly-Asp sequence and hence the ability to inhibit the activity of integrins. Domains A and D are unique and their biochemical or biological activity is unknown. The proposed precursor can be proteolytically cleaved at several interdomain sites, releasing the disintegrins and metalloproteinases. A survey of more than 100 venom metalloproteinases and disintegrins strongly supports the existence of precursor proteins and their structural domains. This is also upheld by the co-occurrence occurrence of metalloproteinases and disintegrins in the venoms of several genera of crotalid and viperid snakes. The likelihood of intradomain disulfide bridges, and accessibility of all interdomain cleavage sites also supports our contention. The susceptibility of the cleavage sites appears to be determined by nearby disulfide bridges and glycosylation. Recognition of the proposed structural domains of venom proteinases should help clarify the structure-function relationships of several related proteins, and influence the synthesis of recombinant disintegrins, metalloproteinases and related polypeptides.