Small serum protein-1 changes the susceptibility of an apoptosis-inducing metalloproteinase HV1 to a metalloproteinase inhibitor in habu snake (Trimeresurus flavoviridis)

Discovery of the Gene Encoding a Novel Small Serum Protein (SSP) of Protobothrops flavoviridis and the Evolution of SSPs

Small serum proteins (SSPs) are low-molecular-weight proteins in snake serum with affinities for various venom proteins. Five SSPs, PfSSP-1 through PfSSP-5, have been reported in Protobothrops flavoviridis (“habu”, Pf) serum so far. Recently, we reported that the five genes encoding these PfSSPs are arranged in tandem on a single chromosome. However, the physiological functions and evolutionary origins of the five SSPs remain poorly understood. In a detailed analysis of the habu draft genome, we found a gene encoding a novel SSP, SSP-6. Structural analysis of the genes encoding SSPs and their genomic arrangement revealed the following: (1) SSP-6 forms a third SSP subgroup; (2) SSP-5 and SSP-6 were present in all snake genomes before the divergence of non-venomous and venomous snakes, while SSP-4 was acquired only by venomous snakes; (3) the composition of paralogous SSP genes in snake genomes seems to reflect snake habitat differences; and (4) the evolutionary emergence of SSP genes is probably related to the physiological functions of SSPs, with an initial snake repertoire of SSP-6 and SSP-5. SSP-4 and its derivative, SSP-3, as well as SSP-1 and SSP-2, appear to be venom-related and were acquired later.

Natural Inhibitors of Snake Venom Metalloproteinases

Snakebites are a hazard in the tropical world. Although antivenom therapy is effective, it is beset with inherent drawbacks. A better understanding of the major components of snake venoms and their neutralisation will help in improving snakebite treatment. Snake venom metalloproteinases (SVMPs) are responsible for severe haemorrhage, the inhibition of coagulation and platelet aggregation, observed in the victims of snakebite envenoming. Inhibitors from various sources including medicinal plants, animal venoms, and sera are sought to block the pharmacological functions of SVMPs. In this review, we describe the interaction of natural inhibitors with SVMPs. To understand their inhibitory mechanisms, we focussed on the complex structures of these inhibitors and SVMPs. There are three distinct classes of inhibitors; namely, chelators, competitive inhibitors, and non-competitive inhibitors. A small number of inhibitors show their anti-hemorrhagic activity in invivo animal models in treatment mode, but most studies evaluate either invitro neutralisation of enzymatic activity or invivo effects in pre-incubation protocols. We propose the distinct strategies and limitations to design either broad-spectrum or highly selective SVMP inhibitors. The goal of designing broad-spectrum inhibitors against SVMPs capable of effective treatment of snakebites without toxicity has been elusive, probably because of the narrow molecular footprint of inhibitors against a large number of SVMPs with distinct molecular surfaces. Our ability to design highly selective inhibitors is limited by the lack of information of interactions between selective inhibitors and SVMPs. Comparisons of structures of hemorrhagic and non-hemorrhagic SVMPs revealed different distributions of electric charge on the surface of SVMPs, which may be exploited to design specific inhibitors. The specific inhibitors may also be useful to identify target molecules of the SVMPs and help to understand their mechanism of action.

Omics Technologies for Profiling Toxin Diversity and Evolution in Snake Venom: Impacts on the Discovery of Therapeutic and Diagnostic Agents

Snake venoms are primarily composed of proteins and peptides, and these toxins have developed high selectivity to their biological targets. This makes venoms interesting for exploration into protein evolution and structure-function relationships. A single venom protein superfamily can exhibit a variety of pharmacological effects; these variations in activity originate from differences in functional sites, domains, posttranslational modifications, and the formations of toxin complexes. In this review, we discuss examples of how the major venom protein superfamilies have diversified, as well as how newer technologies in the omics fields, such as genomics, transcriptomics, and proteomics, can be used to characterize both known and unknown toxins.Because toxins are bioactive molecules with a rich diversity of activities, they can be useful as therapeutic and diagnostic agents, and successful examples of toxin applications in these areas are also reviewed. With the current rapid pace of technology, snake venom research and its applications will only continue to expand.

Unique structure (construction and configuration) and evolution of the array of small serum protein genes of Protobothrops flavoviridis snake

The nucleotide sequence of Protobothrops flavoviridis (Pf) 30534 bp genome segment which contains genes encoding small serum proteins (SSPs) was deciphered. The genome segment contained five SSP genes (PfSSPs), PfSSP-4, PfSSP-5, PfSSP-1, PfSSP-2, and PfSSP-3 in this order and had characteristic configuration and constructions of the particular nucleotide sequences inserted. Comparison between the configurations of the inserted chicken repeat-1 (CR1) fragments of P. flavoviridis and Ophiophagus hannah (Oh) showed that the nucleotide segment encompassing from PfSSP-1 to PfSSP-2 was inverted. The inactive form of PfSSP-1, named PfSSP-1δ(Ψ), found in the intergenic region (I-Reg) between PfSSP-5 and PfSSP-1 had also been destroyed by insertions of the plural long interspersed nuclear elements (LINEs) and DNA transposons. The L2 LINE inserted into the third intron or the particular repetitive sequences inserted into the second intron structurally divided five PfSSPs into two subgroups, the Long SSP subgroup of PfSSP-1, PfSSP-2 and PfSSP-5 or the Short SSP subgroup of PfSSP-3 and PfSSP-4. The mathematical analysis also showed that PfSSPs of the Long SSP subgroup evolved alternately in an accelerated and neutral manner, whereas those of the Short SSP subgroup evolved in an accelerated manner. Moreover, the ortholog analysis of SSPs of various snakes showed that the evolutionary emerging order of SSPs was as follows: SSP-5, SSP-4, SSP-2, SSP-1, and SSP-3. The unique interpretation about accelerated evolution and the novel idea that the transposable elements such as LINEs and DNA transposons are involved in maintaining the host genome besides its own transposition natures were proposed.

Natural Inhibitors of Snake Venom Metalloendopeptidases: History and Current Challenges

The research on natural snake venom metalloendopeptidase inhibitors (SVMPIs) began in the 18th century with the pioneering work of Fontana on the resistance that vipers exhibited to their own venom. During the past 40 years, SVMPIs have been isolated mainly from the sera of resistant animals, and characterized to different extents. They are acidic oligomeric glycoproteins that remain biologically active over a wide range of pH and temperature values. Based on primary structure determination, mammalian plasmatic SVMPIs are classified as members of the immunoglobulin (Ig) supergene protein family, while the one isolated from muscle belongs to the ficolin/opsonin P35 family. On the other hand, SVMPIs from snake plasma have been placed in the cystatin superfamily. These natural antitoxins constitute the first line of defense against snake venoms, inhibiting the catalytic activities of snake venom metalloendopeptidases through the establishment of high-affinity, non-covalent interactions. This review presents a historical account of the field of natural resistance, summarizing its main discoveries and current challenges, which are mostly related to the limitations that preclude three-dimensional structural determinations of these inhibitors using “gold-standard” methods; perspectives on how to circumvent such limitations are presented. Potential applications of these SVMPIs in medicine are also highlighted.

Flavorase, a novel non-haemorrhagic metalloproteinase in Protobothrops flavoviridis venom, is a target molecule of small serum protein-3

Some venomous snakes possess anti-toxic proteins in their sera that may play a role in neutralizing the haemorrhagic factors or toxins in their own venom. Five small serum proteins (SSP-1-SSP-5) were isolated from the serum of Japanese viper (Protobothrops flavoviridis), and were found to act as self-defence proteins against the viper's own toxic components. However, the physiological function of SSP-3 has not been completely elucidated. Affinity chromatography of the venom on an SSP-3-immobilized column identified a novel 55-kDa protein as the target molecule of SSP-3. Sequences of internal fragments of this SSP-3-binding protein showed high homology to those of metalloproteinases from the P. flavoviridis venom. The cDNA sequence revealed that this protein, termed flavorase, is a P-III class metalloproteinase consisting of 423 amino acid residues. The purified protein did not show haemorrhagic and cytotoxic activity. Biacore measurements revealed that SSP-3 was bound to flavorase with a dissociation constant of 6.4 × 10(-9) M. SSP-3 non-competitively inhibited the peptidase activity of flavorase with an inhibition constant of 6.6 × 10(-9) M.

Structural analysis and characterization of new small serum proteins from the serum of a venomous snake (Gloydius blomhoffii)

Some snakes have several anti-toxic proteins in their sera that neutralize their own venom. Five new small serum proteins (SSPs) were isolated from Japanese mamushi (Gloydius blomhoffii) serum by gel-filtration and RP-HPLC, and their N-Terminal sequences were determined. The amino acid sequences of the precursor proteins were deduced from the nucleotide sequences of cDNAs encoding them. Due to the sequence similarity to those of SSPs in habu snake (Protobothrops flavoviridis) serum (>75% identity), these proteins were designated mSSP-1 to mSSP-5 as the homologs of habu proteins. mSSP-1 was stable at 100 °C and in the pH range of 1-10, and inhibited the proteolytic activity of a certain snake venom metalloproteinase. The inhibitory activity was extinguished by modifying the amino groups of mSSP-1. mSSP-1 is the first prostate secretory protein of the 94 amino acid-family protein with a carbohydrate chain in the Asn37 residue.