Crystallization and preliminary X-ray analysis of a Kunitz-type inhibitor, textilinin-1 from Pseudonaja textilis textilis

Analysis of Kunitz inhibitors from plants for comprehensive structural and functional insights

Legume Kunitz type trypsin inhibitor (KTI) family is one of the most versatile families of proteins. A typical KTI features a single peptide folded in β-trefoil manner, with the molecular weight about 20-22kDa and two disulphide bonds. The members are known to inhibit a wide range of serpins proteases at the same time many of them possess unique features. Copaifera langsdorffii Trypsin inhibitor (CTI) has a β-trefoil fold made up of two non-covalently bound polypeptide chains with only a single disulfide bridge. Delonix regia Trypsin inhibitor (DrTI) has one amino acid insertion between P1 and P2 of the reactive site distorting its conformation. Bauhinia bauhinioides Cruzipain inhibitor (BbCI) has a conservative β-trefoil fold but lacks disulfide bonds. Such subtle differences in structures make Kunitz inhibitors different from other inhibitor families. Most of the studies on these inhibitors are focused towards their proposed role in defense from insect pests and wounding but their exact physiological role in nature is still uncharted. Thus, it would be very interesting to closely analyze the structural details of these inhibitors in order to ascertain their biological role and other fascinating applications.

Proteomic comparisons of venoms of long-term captive and recently wild-caught Eastern brown snakes (Pseudonaja textilis) indicate venom does not change due to captivity

Snake venom is a highly variable phenotypic character, and its variation and rapid evolution are important because of human health implications. Because much snake antivenom is produced from captive animals, understanding the effects of captivity on venom composition is important. Here, we have evaluated toxin profiles from six long-term (LT) captive and six recently wild-caught (RC) eastern brown snakes, Pseudonaja textilis, utilizing gel electrophoresis, HPLC-MS, and shotgun proteomics. We identified proteins belonging to the three-finger toxins, group C prothrombin activators, Kunitz-type serine protease inhibitors, and phospholipases A2, among others. Although crude venom HPLC analysis showed LT snakes to be higher in some small molecular weight toxins, presence/absence patterns showed no correlation with time in captivity. Shotgun proteomics indicated the presence of similar toxin families among individuals but with variation in protein species. Although no venom sample contained all the phospholipase A2 subunits that form the textilotoxin, all did contain both prothrombin activator subunits. This study indicates that captivity has limited effects on venom composition, that venom variation is high, and that venom composition may be correlated to geographic distribution.

BIOLOGICAL SIGNIFICANCE

Through proteomic comparisons, we show that protein variation within LT and RC groups of snakes (Pseudonaja textilis) is high, thereby resulting in no discernible differences in venom composition between groups. We utilize complementary techniques to characterize the venom proteomes of 12 individual snakes from our study area, and indicate that individuals captured close to one another have more similar venom gel electrophoresis patterns than those captured at more distant locations. These data are important for understanding natural variation in and potential effects of captivity on venom composition.

Cloning, characterization and phylogenetic analyses of members of three major venom families from a single specimen of Walterinnesia aegyptia

Walterinnesia aegyptia is a monotypic elapid snake inhabiting in Africa and Mideast. Although its envenoming is known to cause rapid deaths and paralysis, structural data of its venom proteins are rather limited. Using gel filtration and reverse-phase HPLC, phospholipases A(2) (PLAs), three-fingered toxins (3FTxs), and Kunitz-type protease inhibitors (KIns) were purified from the venom of a single specimen of this species caught in northern Egypt. In addition, specific primers were designed and PCR was carried out to amplify the cDNAs encoding members of the three venom families, respectively, using total cDNA prepared from its venom glands. Complete amino acid sequences of two acidic PLAs, three short chain 3FTxs, and four KIns of this venom species were thus deduced after their cDNAs were cloned and sequenced. They are all novel sequences and match the mass data of purified proteins. For members of each toxin family, protein sequences were aligned and subjected to molecular phylogenetic analyses. The results indicated that the PLAs and a Kunitz inhibitor of W. aegyptia are most similar to those of king cobra venom, and its 3FTxs belongs to either Type I alpha-neurotoxins or weak toxins of orphan-II subtype. It is remarkable that both king cobra and W. aegyptia cause rapid deaths of the victims, and a close evolutionary relationship between them is speculated.