At present, they form one of the largest toxin families and their number is increasing constantly. and some muscarinic toxins have been shown to interact with adrenoceptors. New, unexpected activities have been demonstrated for some TFTs as well, such as toxin interaction with interleukin or insulin receptors and even TFT-activated motility of sperm. This minireview provides a summarization of the data that has emerged in the last decade on the TFTs and their activities. cobra venom. Determination of the homodimer crystal structure allowed identification of the intermolecular disulfides formed by Cys3 in the protomer one and Cys20 in the protomer two, and other way round (Figure ?(Figure1A).1A). All other disulfides in protomers had the same pairing as in natural -CTX. Open in a separate window Figure 1 Spatial structures of dimeric three-finger Lixisenatide toxins. A: Homodimer of -cobratoxin, Protein Data Bank Identification code (PDB ID): 4AEA; B: Irditoxin, PDB ID: 2H7Z; C: Haditoxin, PDB ID: 3HH7; D: -bungarotoxin, PDB ID: 1KBA. Disulfide bonds are shown in yellow. N and C indicate N- and C-terminus, respectively. The dimerization itself strongly affected the biological activity of the original toxins, with the cytotoxic activity of cytotoxins within dimers being completely abolished. However, the dimers were found to retain most of the -CTX capacity to interact with and 7 nAChRs as well as with the acetylcholine-binding protein. Moreover, in contrast to the -CTX monomer, the -CTX dimer acquired the capacity Lixisenatide to interact Lixisenatide with 32 nAChR, similar to that seen with -bungarotoxin (-Bgt), a dimer with no disulfides between its monomers (Figure ?(Figure1D).1D). Collectively, these data show that dimerization of three-fingered neurotoxins is essential for binding to heteromeric 32 nAChRs. In 2009 2009, from venom of the brown cat snake a new heterodimeric TFT, irditoxin, was isolated. Irditoxin spatial structure determined by X-ray analysis displayed two subunits possessing a three-finger fold, characteristic for nonconventional toxins (Figure ?(Figure1B).1B). The subunits in the irditoxin dimer are connected by an interchain disulfide bond, formed by extra cysteine residues present in each subunit. In contrast to the dimeric toxins discussed above, irditoxin does not inhibit mouse neuronal 32 and 7 nAChRs. However, irditoxin is a bird- and reptile-specific postsynaptic neurotoxin which inhibits the chick muscle nAChR three orders of magnitude more efficiently than the mouse receptor. (Eastern green mamba); 3NOJ_BUNCA: Bucandin from (Malayan krait); 3NOJ6_DENJA: Toxin S6C6 from (Eastern Lixisenatide Jameson’s mamba); 3NOJ_WALAE: Actiflagelin from (desert black snake). Several new TFTs retaining the classical arrangement of disulfide bonds but possessing novel structural features have been identified recently. So, from the venom of black mamba venom may represent a new group of competitive nAChR antagonists, known as the -neurotoxins. Electrophysiology experiments on oocytes showed that Oh9-1 inhibited rat muscle-type 11 (adult, IC50 3.1 mol/L) and11 (fetal, IC50 5.6 mol/L) and rat neuronal 32 nAChRs (IC50 50.2 mol/L), but manifested low or no affinity for other human and rat neuronal subtypes. Interestingly, Oh9-1 potentiated the human Rabbit Polyclonal to Tip60 (phospho-Ser90) glycine receptor (homopentamer composed of 1 subunits), with activity increase by about 2-fold. Alanine-scan mutagenesis showed a novel mode of interaction with the ACh binding pocket of nAChRs a set of functional amino acid residues that are different from those in the classical -neurotoxins. Herewith, the central loop of Oh9-1 interacts with 11 nAChR by both sides of the -strand, while only one side of the -strand interacts with the 32 receptor. The taxon-specific dimeric TFT irditoxin, isolated from a rear-fanged snake, was discussed above. Another taxon-specific TFT, fulgimotoxin, was isolated from the venom of the rear-fanged green vine snake venom. Earlier studies of biological activity revealed no interaction with the muscarinic acetylcholine receptors (mAChRs) M1 and M2 nor with the muscle-type nAChR. However, recent studies showed that BMLCL interacted efficiently with both 7 (IC50 43 nmol/L) and muscle-type nAChR (IC50 31 nmol/L). Thus, the longest TFT functions as an antagonist of nAChRs. It should be noted that so Lixisenatide far, no TFTs have been found in the venoms of snakes from the family; however, transcripts encoding these toxins were identified in venom gland transcriptomes of several species. To address the question of biological activity of TFTs, two toxins were obtained by heterologous expression in and TFT (TFT-AF) and TFT (VN-TFT), both of the nonconventional type, were refolded under the conditions elaborated on earlier for cobra TFTs. The biological activity of the.