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.
Highlights
The Small conductance calcium-activated Kϩ (SK) channel mechanism that controls scorpion toxin recognition remains unknown
The SK3 Channel Is Selectively Inhibited by Specific Scorpion Toxins Exhibiting No More than Three Basic Amino Acid Residues in Their Channel-binding Interfaces—As shown, the SK3 channels were almost insensitive to a 100 nM concentration of many types of the potassium channel-active ChTX toxin (Fig. 2A) or the Kv channel-active ADWX-1 peptide (Fig. 2B) [29]
The channel-binding interface of BmP05 or scyllatoxin presents only three (Fig. 2G) or two (Fig. 2H) basic residues [33, 34]. These structural differences in channel-binding interfaces suggest that the SK3 channel may be selectively recognized by scorpion toxins possessing three basic residues in these critical positions
Summary
The SK channel mechanism that controls scorpion toxin recognition remains unknown. Results: Two conserved arginine residues in the SK3 channel outer vestibule were found to control toxin recognition. 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. 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, located in the SK3 channel outer vestibule, were identified as being critical for toxin affinity. In contrast to the Kv1.2 extracellular pore entryway structure, the large turret and unusual TIGYGLR sequence in the filter region of Kir2.2 are responsible for its relative insensitivity to Kϩ channel toxins [6, 7]. Acidic amino acid residues of toxins were found to affect the interac-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
