title: Addition of positive charges at the C-terminal peptide region of CssII, a mammalian scorpion peptide toxin, improves its affinity for sodium channels Nav1.6.
abstract: CssII is a β-scorpion peptide that modifies preferentially sodium currents of the voltage-dependent Na(+) channel (Nav) sub-type 1.6. Previously, we have found that the C-terminal amidation of CssII increases its affinity for Nav, which opens at more negative potentials in the presence of CssII. Although C-terminal amidation in vitro conditions is possible, five CssII peptide toxin variants with C-terminal residues modified were heterologously expressed (rN66S, rN66H, rN66R, r[T64R/N66S] and r[T64R/N66R], in which r stands for recombinant, the capital letters to the amino acid residues and the numbers indicate the position of the given residue into the primary sequence of the toxin) and correctly folded. A secondary structure prediction of CssII agrees with the experimental secondary structure obtained by circular dichroism; so all bacterial expressed neurotoxin variants maintained the typical α/β secondary structure motif of most Na(+) channel scorpion toxins. The electrophysiological properties of all recombinant variants were examined, and it was found that substitutions of threonine (T) and asparagine (N) at the C-terminal region for arginine (R) (r[T64R/N66R]) increase their affinity for Nav1.6. Although, the molecular interactions involved in this mechanism are still not clearly determined, there is experimental evidence supporting the suspicion that incorporation of basic charged amino acid residues at the C-terminal tail of a group of α-scorpion toxin was favored by natural selection.
authors.affiliation: Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, UNAM, Av. Universidad 2001, Apartado Postal 510-3, Cuernavaca, Morelos 61500, Mexico.
authors.forename: Georgina
authors.initials: G
authors.lastname: Estrada
authors.forename: Rita
authors.initials: R
authors.lastname: Restano-Cassulini
authors.forename: Ernesto
authors.initials: E
authors.lastname: Ortiz
authors.forename: Lourival D
authors.initials: LD
authors.lastname: Possani
authors.forename: Gerardo
authors.initials: G
authors.lastname: Corzo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D008969:Molecular Sequence Data; D062557:NAV1.6 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D012604:Scorpion Venoms / Q000737:chemistry* / Q000378:metabolism; D012605:Scorpions / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry / Q000378:metabolism*
chemical_list: D062557:NAV1.6 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; C100681:SCN8A protein, human; D012604:Scorpion Venoms; D015222:Sodium Channels; C066386:scorpion toxin Css II