title: Structure-activity relationship of an alpha-toxin Bs-Tx28 from scorpion (Buthus sindicus) venom suggests a new alpha-toxin subfamily.
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 alpha-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 alpha-neurotoxins, active against receptor site-3 of mammalian (e.g., Lqq-IV and Lqh-IV from scorpions Leiurus sp.) and insect (e.g., BJalpha-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 alpha- and alpha-like toxins suggests the presence of a new and separate subfamily of scorpion alpha-toxins. Bs-Tx28 which is weakly active in both, mammals and insects (LD(50) 0.088 and 14.3microg/g, respectively), shows strong induction of the rat afferent nerve discharge in a dose-dependent fashion (EC(50)=0.01microg/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 alpha-mammal (AaH-II), alpha-insect (Lqh-alphaIT), and alpha-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 alpha-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 alpha-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 alpha-mammal toxins.
authors.affiliation: International Center for Chemical Sciences, HEJ Research Institute of Chemistry, University of Karachi, Karachi 75270, Pakistan. syedabid_ali@yahoo.com
authors.forename: Syed Abid
authors.initials: SA
authors.lastname: Ali
authors.forename: Bingxian
authors.initials: B
authors.lastname: Wang
authors.forename: Mehtab
authors.initials: M
authors.lastname: Alam
authors.forename: Alexander
authors.initials: A
authors.lastname: Beck
authors.forename: Stanka
authors.initials: S
authors.lastname: Stoeva
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Voelter
authors.forename: Atiya
authors.initials: A
authors.lastname: Abbasi
authors.forename: Michael
authors.initials: M
authors.lastname: Duszenko
mesh_terms: D000200:Action Potentials; D000595:Amino Acid Sequence; D000818:Animals; D020048:Blattellidae; D002942:Circular Dichroism; D005769:Gastrointestinal Motility; D066298:In Vitro Techniques; D007583:Jejunum / Q000187:drug effects / Q000294:innervation / Q000502:physiology; D007928:Lethal Dose 50; D008638:Mesenteric Arteries / Q000294:innervation; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000737:chemistry* / Q000633:toxicity; D010802:Phylogeny; D011487:Protein Conformation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012604:Scorpion Venoms / Q000737:chemistry* / Q000633:toxicity; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D026941:Sodium Channel Blockers / Q000737:chemistry / Q000633:toxicity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013329:Structure-Activity Relationship; D013779:Tetrodotoxin / Q000737:chemistry / Q000378:metabolism
chemical_list: D009498:Neurotoxins; D012604:Scorpion Venoms; D026941:Sodium Channel Blockers; C508329:alpha-toxin Bs-Tx28; D013779:Tetrodotoxin