title: Structural and functional differences of two toxins from the scorpion Pandinus imperator.
abstract: The Pandinotoxins, PiTX-K alpha and PiTX-K beta, are members of the Charybdotoxin family of scorpion toxins that can be used to characterize K+ channels. PiTX-K alpha differs from PiTX-K beta, another peptide from Pandinus imperator, by one residue (P10E). When the two toxins are compared in a physiological assay, the affinity of PiTX-K beta for voltage-gated, rapidly inactivating K+ channels in dorsal root ganglia (DRG) neurons is 800-fold lower than that of PiTX-K alpha (K alpha-IC50 = 8.0 nM versus K beta-IC50 = 6,500 nM). To understand this difference, the three-dimensional structure of PiTX-K beta was determined by nuclear magnetic resonance (NMR) spectroscopy and compared to that of PiTX-K alpha. This comparison shows that structural differences between the two toxins occur at a residue that is critical for blocking K+ channels (K27) as well as at the site of the natural mutation (P10E). In PiTX-K beta, the negatively charged carboxylate oxygen of E10 can approach the positive charge of K27 and presumably reduces the net positive charge in this region of the toxin. This is likely the reason why PiTX-K beta binds K+ channels from DRG neurons with a much lower affinity than does PiTX-K alpha.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Klenk
authors.forename: T C
authors.initials: TC
authors.lastname: Tenenholz
authors.forename: D R
authors.initials: DR
authors.lastname: Matteson
authors.forename: R S
authors.initials: RS
authors.lastname: Rogowski
authors.forename: M P
authors.initials: MP
authors.lastname: Blaustein
authors.forename: D J
authors.initials: DJ
authors.lastname: Weber
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018999:Charybdotoxin / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015221:Potassium Channels / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D012604:Scorpion Venoms / Q000737:chemistry*; D012605:Scorpions / Q000737:chemistry*; D016415:Sequence Alignment; D055672:Static Electricity; D014118:Toxins, Biological / Q000737:chemistry*
chemical_list: C105110:Pandinus toxin K-alpha; D015221:Potassium Channels; D011994:Recombinant Proteins; D012604:Scorpion Venoms; D014118:Toxins, Biological; D018999:Charybdotoxin; C087603:agitoxin 2