Article ID Journal Published Year Pages File Type
1927646 Archives of Biochemistry and Biophysics 2006 14 Pages PDF
Abstract

Scorpion venoms are among the most widely known source of peptidyl neurotoxins used for callipering different ion channels, e.g., for Na+, K+, Ca+ or Cl−. An α-toxin (Bs-Tx28) has been purified from the venom of scorpion Buthus sindicus, a common yellow scorpion of Sindh, Pakistan. The primary structure of Bs-Tx28 was established using a combination of MALDI-TOF-MS, LC-ESI-MS, and automated Edman degradation analysis. Bs-Tx28 consists of 65 amino acid residues (7274.3 ± 2Da), including eight cysteine residues, and shows very high sequence identity (82–94%) with other long-chain α-neurotoxins, active against receptor site-3 of mammalian (e.g., Lqq-IV and Lqh-IV from scorpions Leiurus sp.) and insect (e.g., BJα-IT and Od-1 from Buthotus judaicus and Odonthobuthus doriae, respectively) voltage-gated Na+ channels. Multiple sequence alignment and phylogenetic analysis of Bs-Tx28 with other known α- and α-like toxins suggests the presence of a new and separate subfamily of scorpion α-toxins. Bs-Tx28 which is weakly active in both, mammals and insects (LD50 0.088 and 14.3 μg/g, respectively), shows strong induction of the rat afferent nerve discharge in a dose-dependent fashion (EC50 = 0.01 μg/mL) which was completely abolished in the presence of tetrodotoxin suggesting the binding of Bs-Tx28 to the TTX-sensitive Na+-channel. Three-dimensional structural features of Bs-Tx28, established by homology modeling, were compared with other known classical α-mammal (AaH-II), α-insect (Lqh-αIT), and α-like (BmK-M4) toxins and revealed subtle variations in the Nt-, Core-, and RT-CT-domains (functional domains) which constitute a “necklace-like” structure differing significantly in all α-toxin subfamilies. On the other hand, a high level of conservation has been observed in the conserved hydrophobic surface with the only substitution of W43 (Y43/42) and an additional hydrophobic character at position F40 (L40/A/V/G39), as compared to the other mentioned α-toxins. Despite major differences within the primary structure and activities of Bs-Tx28, it shares a common structural and functional motif (e.g., transRT-farCT) within the RT-CT domain which is characteristic of scorpion α-mammal toxins.

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