Structure and Activity of α-Conotoxin PeIA at Nicotinic Acetylcholine Receptor Subtypes and GABAB Receptor-coupled N-type Calcium Channels

Abstract

␣-Conotoxins are peptides from cone snails that target the nicotinic acetylcholine receptor (nAChR). RgIA and Vc1.1 have analgesic activity in animal pain models. Both peptides target the ␣9␣10 nAChR and inhibit N-type calcium channels via GABA B receptor activation, but the mechanism of action of analgesic activity is unknown. PeIA has previously been shown to inhibit the ␣9␣10 and ␣3␤2 nAChRs. In this study, we have determined the structure of PeIA and shown that it is also a potent inhibitor of N-type calcium channels via GABA B receptor activation. The characteristic ␣-conotoxin fold is present in PeIA, but it has a different distribution of surface-exposed hydrophobic and charged residues compared with Vc1.1. Thus, the surface residue distribution, rather than the overall fold, appears to be responsible for the 50-fold increase in selectivity at the ␣3␤2 nAChR by PeIA relative to Vc1.1. In contrast to their difference in potency at the nAChR, the equipotent activity of PeIA and Vc1.1 at the GABA B receptor suggests that the GABA B receptor is more tolerant to changes in surface residues than is the nAChR. The conserved Asp-Pro-Arg motif of Vc1.1 and RgIA, which is crucial for potency at the ␣9␣10 nAChR, is not required for activity at GABA B receptor/N-type calcium channels because PeIA has a His-Pro-Ala motif in the equivalent position. This study shows that different structure-activity relationships are associated with the targeting of the GABA B receptor versus nAChRs. Furthermore, there is probably a much more diverse range of conotoxins that target the GABA B receptor than currently realized.

Cloning, synthesis, and characterization of αO-conotoxin GeXIVA, a potent α9α10 nicotinic acetylcholine receptor antagonist

“…Analgesic effects occurred at low doses (2 nmol or lower), with the 2-nmol dose producing effects greater than or equal to a dose of 500 nmol of the opioid analgesic morphine. Several studies have shown that some α-conotoxins block VGCCs via stimulation of GABA B receptors, suggesting that antinociceptive effects were mediated through blockade of N-type calcium channels (28)(29)(30)(31)(32)(33). However, some studies have not fully reproduced this effect (34,35), and we show that GeXIVA fails to block VGCCs.…”

α-Conotoxin PeIA[S9H,V10A,E14N] Potently and Selectively Blocks α6β2β3 versus α6β4 Nicotinic Acetylcholine Receptors

“…1A). Despite their sequence differences, molecular modeling and solution NMR studies predict that PeIA, MII, and PnIA all share a similar three-dimensional backbone structure and occupy the acetylcholine binding pocket in approximately the same orientation (Rogers et al, 1999;Daly et al, 2011;Pucci et al, 2011). These differences and similarities suggest that specific residues of the peptides might be critical for binding to ␣6␤2-containing nAChRs.…”

“…PeIA[S9H,V10A,E14N] was generated using the NMR structural coordinates of PeIA (Daly et al, 2011) as a template and the mutagenesis function of PyMOL. MII was also generated from NMR structural coordinates (Hill et al, 1998), and PnIA was generated from X-ray crystallography coordinates (Hu et al, 1996).…”

Structure–Activity Studies of Cysteine‐Rich α‐Conotoxins that Inhibit High‐Voltage‐Activated Calcium Channels via GABAB Receptor Activation Reveal a Minimal Functional Motif

“…[6] Vc1.1 and RgIA are a9a10 nAChR subtype antagonists,and potently inhibit N-type (Ca v 2.2) and R-type (Ca v 2.3) calcium channels via GABA B receptor (GABA B R) activation. [8] Subsequently,t hree other conotoxins,P eIA, [9] AuIB [5d] and Vc1.2, [10] have also been shown to inhibit HVAc alcium channels via aGABA B R-dependent mechanism ( Figure 1A). [8] Subsequently,t hree other conotoxins,P eIA, [9] AuIB [5d] and Vc1.2, [10] have also been shown to inhibit HVAc alcium channels via aGABA B R-dependent mechanism ( Figure 1A).…”