Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic Strength
κ-Conotoxin-PVIIA (κ-PVIIA) is a potassium-channel blocking peptide from the venom of the fish-hunting snail, <i>Conus purpurascens</i>, which is essential for quick prey’s excitotoxic immobilization. Binding of one κ-PVIIA to <i>Shaker</i> K-channels occludes the K<sup>...
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2020-10-01
|
| Series: | Marine Drugs |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1660-3397/18/11/533 |
| _version_ | 1827703461341298688 |
|---|---|
| author | David Naranjo Ignacio Díaz-Franulic |
| author_facet | David Naranjo Ignacio Díaz-Franulic |
| author_sort | David Naranjo |
| collection | DOAJ |
| description | κ-Conotoxin-PVIIA (κ-PVIIA) is a potassium-channel blocking peptide from the venom of the fish-hunting snail, <i>Conus purpurascens</i>, which is essential for quick prey’s excitotoxic immobilization. Binding of one κ-PVIIA to <i>Shaker</i> K-channels occludes the K<sup>+</sup>-conduction pore without additional conformational effects. Because this 27-residue toxin is +4-charged at neutral pH, we asked if electrostatic interactions play a role in binding. With Voltage-Clamp electrophysiology, we tested how ionic strength (IS) affects κ-PVIIA blockade to <i>Shaker</i>. When IS varied from ~0.06 to ~0.16 M, the dissociation constant for open and closed channels increased by ~5- and ~16-fold, respectively. While the association rates decreased equally, by ~4-fold, in open and closed channels, the dissociation rates increased 4–5-fold in closed channels but was IS-insensitive in open channels. To explain this differential IS-dependency, we propose that the bound κ-PVIIA wobbles, so that in open channels the intracellular environment, via ion-conduction pore, buffers the imposed IS-changes in the toxin-channel interface. A Brønsted-Bjerrum analysis on the rates predicts that if, instead of fish, the snail preyed on organisms with seawater-like lymph ionic composition, a severely harmless toxin, with >100-fold diminished affinity, would result. Thus, considerations of the native ionic environment are essential for conotoxins evaluation as pharmacological leads. |
| first_indexed | 2024-03-10T15:19:27Z |
| format | Article |
| id | doaj.art-1bea5437784a486baed2d8c6c3edd37a |
| institution | Directory Open Access Journal |
| issn | 1660-3397 |
| language | English |
| last_indexed | 2024-03-10T15:19:27Z |
| publishDate | 2020-10-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Marine Drugs |
| spelling | doaj.art-1bea5437784a486baed2d8c6c3edd37a2023-11-20T18:37:37ZengMDPI AGMarine Drugs1660-33972020-10-01181153310.3390/md18110533Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic StrengthDavid Naranjo0Ignacio Díaz-Franulic1Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360103, ChileCenter for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Santiago 8370146, Chileκ-Conotoxin-PVIIA (κ-PVIIA) is a potassium-channel blocking peptide from the venom of the fish-hunting snail, <i>Conus purpurascens</i>, which is essential for quick prey’s excitotoxic immobilization. Binding of one κ-PVIIA to <i>Shaker</i> K-channels occludes the K<sup>+</sup>-conduction pore without additional conformational effects. Because this 27-residue toxin is +4-charged at neutral pH, we asked if electrostatic interactions play a role in binding. With Voltage-Clamp electrophysiology, we tested how ionic strength (IS) affects κ-PVIIA blockade to <i>Shaker</i>. When IS varied from ~0.06 to ~0.16 M, the dissociation constant for open and closed channels increased by ~5- and ~16-fold, respectively. While the association rates decreased equally, by ~4-fold, in open and closed channels, the dissociation rates increased 4–5-fold in closed channels but was IS-insensitive in open channels. To explain this differential IS-dependency, we propose that the bound κ-PVIIA wobbles, so that in open channels the intracellular environment, via ion-conduction pore, buffers the imposed IS-changes in the toxin-channel interface. A Brønsted-Bjerrum analysis on the rates predicts that if, instead of fish, the snail preyed on organisms with seawater-like lymph ionic composition, a severely harmless toxin, with >100-fold diminished affinity, would result. Thus, considerations of the native ionic environment are essential for conotoxins evaluation as pharmacological leads.https://www.mdpi.com/1660-3397/18/11/533Kv-channelpeptide toxinconotoxinassociation ratedissociation rateBrønsted-Bjerrum equation |
| spellingShingle | David Naranjo Ignacio Díaz-Franulic Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic Strength Marine Drugs Kv-channel peptide toxin conotoxin association rate dissociation rate Brønsted-Bjerrum equation |
| title | Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic Strength |
| title_full | Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic Strength |
| title_fullStr | Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic Strength |
| title_full_unstemmed | Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic Strength |
| title_short | Binding of κ-Conotoxin-PVIIA to Open and Closed Shaker K-Channels Are Differentially Affected by the Ionic Strength |
| title_sort | binding of κ conotoxin pviia to open and closed shaker k channels are differentially affected by the ionic strength |
| topic | Kv-channel peptide toxin conotoxin association rate dissociation rate Brønsted-Bjerrum equation |
| url | https://www.mdpi.com/1660-3397/18/11/533 |
| work_keys_str_mv | AT davidnaranjo bindingofkconotoxinpviiatoopenandclosedshakerkchannelsaredifferentiallyaffectedbytheionicstrength AT ignaciodiazfranulic bindingofkconotoxinpviiatoopenandclosedshakerkchannelsaredifferentiallyaffectedbytheionicstrength |