αS-conotoxin GVIIIB potently and selectively blocks (α9α10 nicotinic acetylcholine receptors

Although acetylcholine is widely utilized in vertebrate nervous systems, nicotinic acetylcholine receptors (nAChRs), including the alpha 9 alpha 10 subtype, also are expressed in a wide variety of non-neuronal cells. These cell types include cochlear hair cells, adrenal chromaffin cells and immune cells. alpha 9 alpha 10 nAChRs present in these cells may respectively play roles in protection from noise-induced hearing loss, response to stress and neuroprotection. Despite these critical functions, there are few available selective ligands to confirm mechanistic hypothesis regarding the role of alpha 9 alpha 10 nAChRs. Conus, has been a rich source of ligands for receptors and ion channels. Here, we identified Corms geographus venom as a lead source for a novel alpha 9 alpha 10 antagonist. The active component was isolated and the encoding gene cloned. The peptide signal sequence and cysteine arrangement had the signature of the sigma-conotoxin superfamily. Previously isolated sigma-conotoxin GVIIIA, also from Conus geographus, targets the 5-HT3 receptor. In contrast, alpha S-GVIIIB blocked the alpha 9 alpha 10 nAChR with an IC50 of 9.8 nM, yet was inactive at the 5-HT3 receptor. Pharmacological characterization of aS-GVIIIB shows that it is over 100-fold selective for the alpha 9 alpha 10 nAChR compared to other nAChR subtypes. Thus, the S-superfamily represents a novel conotoxin scaffold for flexibly targeting a variety of receptor subtypes. Functional competition studies utilized distinct off-rate kinetics of conotoxins to identify the alpha 10/alpha 9 nAChR interface as the site of aS-GVIIIB binding; this adds to the importance of the (+) face of the alpha 10 rather than the (+) face of the alpha 9 nAChR subunit as critical to binding of alpha 9 alpha 10-targeted conotoxins. (C) 2015 Elsevier Inc. All rights reserved.