title: Two conserved arginine residues from the SK3 potassium channel outer vestibule control selectivity of recognition by scorpion toxins.
abstract: Potassium channel functions are often deciphered by using selective and potent scorpion toxins. Among these toxins, only a limited subset is capable of selectively blocking small conductance Ca(2+)-activated K(+) (SK) channels. The structural bases of this selective SK channel recognition remain unclear. In this work, we demonstrate the key role of the electric charges of two conserved arginine residues (Arg-485 and Arg-489) from the SK3 channel outer vestibule in the selective recognition by the SK3-blocking BmP05 toxin. Indeed, individually substituting these residues with histidyl or lysyl (maintaining the positive electric charge partially or fully), although decreasing BmP05 affinity, still preserved the toxin sensitivity profile of the SK3 channel (as evidenced by the lack of recognition by many other types of potassium channel-sensitive charybdotoxin). In contrast, when Arg-485 or Arg-489 of the SK3 channel was mutated to an acidic (Glu) or alcoholic (Ser) amino acid residue, the channel lost its sensitivity to BmP05 and became susceptible to the "new" blocking activity by charybdotoxin. In addition to these SK3 channel basic residues important for sensitivity, two acidic residues, Asp-492 and Asp-518, also located in the SK3 channel outer vestibule, were identified as being critical for toxin affinity. Furthermore, molecular modeling data indicate the existence of a compact SK3 channel turret conformation (like a peptide screener), where the basic rings of Arg-485 and Arg-489 are stabilized by strong ionic interactions with Asp-492 and Asp-518. In conclusion, the unique properties of Arg-485 and Arg-489 (spatial orientations and molecular interactions) in the SK3 channel account for its toxin sensitivity profile.
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Feng
authors.forename: Youtian
authors.initials: Y
authors.lastname: Hu
authors.forename: Hong
authors.initials: H
authors.lastname: Yi
authors.forename: Shijin
authors.initials: S
authors.lastname: Yin
authors.forename: Song
authors.initials: S
authors.lastname: Han
authors.forename: Jun
authors.initials: J
authors.lastname: Hu
authors.forename: Zongyun
authors.initials: Z
authors.lastname: Chen
authors.forename: Weishan
authors.initials: W
authors.lastname: Yang
authors.forename: Zhijian
authors.initials: Z
authors.lastname: Cao
authors.forename: Michel
authors.initials: M
authors.lastname: De Waard
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Sabatier
authors.forename: Wenxin
authors.initials: W
authors.lastname: Li
authors.forename: Yingliang
authors.initials: Y
authors.lastname: Wu
mesh_terms: D001120:Arginine / Q000235:genetics / Q000378:metabolism*; D018999:Charybdotoxin / Q000737:chemistry / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D012604:Scorpion Venoms / Q000737:chemistry* / Q000378:metabolism; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C106380:BmP05 toxin; C406328:KCNN3 protein, human; D012604:Scorpion Venoms; D051640:Small-Conductance Calcium-Activated Potassium Channels; D018999:Charybdotoxin; D001120:Arginine
keywords: Ion Channels; Molecular Docking; Molecular Modeling; Patch Clamp; Potassium Channels; Protein Structure; Protein/Protein Interactions; Toxins