A Single Amino Acid Replacement Boosts the Analgesic Activity of α-Conotoxin AuIB through the Inhibition of the GABABR-Coupled N-Type Calcium Channel

Abstract

α-conotoxin AuIB is the only one of the 4/6 type α-conotoxins (α-CTxs) that inhibits the γ-aminobutyric acid receptor B (GABABR)-coupled N-type calcium channel (CaV2.2). To improve its inhibitory activity, a series of variants were synthesized and evaluated according to the structure–activity relationships of 4/7 type α-CTxs targeting GABABR-coupled CaV2.2. Surprisingly, only the substitution of Pro7 with Arg results in a 2–3-fold increase in the inhibition of GABABR-coupled CaV2.2 (IC50 is 0.74 nM); substitutions of position 9–12 with basic or hydrophobic amino acid and the addition of hydrophobic amino acid Leu or Ile at the second loop to mimic 4/7 type α-CTxs all failed to improve the inhibitory activity of AuIB against GABABR-coupled CaV2.2. Interestingly, the most potent form of AuIB[P7R] has disulfide bridges of “1–4, 2–3” (ribbon), which differs from the “1–3, 2–4” (globular) in the isoforms of wildtype AuIB. In addition, AuIB[P7R](globular) displays potent analgesic activity in the acetic acid writhing model and the partial sciatic nerve injury (PNL) model. Our study demonstrated that 4/6 type α-CTxs, with the disulfide bridge connectivity “1–4, 2–3,” are also potent inhibitors for GABABR-coupled CaV2.2, exhibiting potent analgesic activity.

Marine natural products

“…Exploration of the structure–activity relationship of the α-conotoxin AuIB, originally isolated from Conus aulicus , has identified a variant with the Pro7 residue changed to arginine and an alternative disulfide connectivity that is a potent inhibitor of GABA B R-coupled Ca V 2.2 channels and exhibits in vivo analgesic activity. 577 Comparative evaluation of μ-conotoxins SxIIIC, SmIIIA, and KIIIA in patch-clamp and receptor-based studies has identified that the number of residues in loop 3 can influence the peptides ability to inhibit human voltage-gated sodium hNa V 1.7 channels. 578 Five peptides were purified from the venom of Conus marmoreus – notably, none of the peptides contained disulfide bonds, and they were inactive towards a panel of rat nAChR subtypes.…”