Conotoxins (Ctx) form a large family of peptide toxins from cone snail venoms that act on a broad spectrum of ion channels and receptors. The subgroup alpha-Ctx specifically and selectively binds to subtypes of nicotinic acetylcholine receptors (nAChRs), which are targets for treatment of several neurological disorders. Here we present the structure at a resolution of 2.4 A of alpha-Ctx PnIA (A10L D14K), a potent blocker of the alpha(7)-nAChR, bound with high affinity to acetylcholine binding protein (AChBP), the prototype for the ligand-binding domains of the nAChR superfamily. Alpha-Ctx is buried deep within the ligand-binding site and interacts with residues on both faces of adjacent subunits. The toxin itself does not change conformation, but displaces the C loop of AChBP and induces a rigid-body subunit movement. Knowledge of these contacts could facilitate the rational design of drug leads using the Ctx framework and may lead to compounds with increased receptor subtype selectivity.

Nicotine dependence is linked to single nucleotide polymorphisms in the CHRNB4-CHRNA3-CHRNA5 gene cluster encoding the α3β4α5 nicotinic acetylcholine receptor (nAChR). Here we show that the β4 subunit is rate limiting for receptor activity, and that current increase by β4 is maximally competed by one of the most frequent variants associated with tobacco usage (D398N in α5). We identify a β4-specific residue (S435), mapping to the intracellular vestibule of the α3β4α5 receptor in close proximity to α5 D398N, that is essential for its ability to increase currents. Transgenic mice with targeted overexpression of Chrnb4 to endogenous sites display a strong aversion to nicotine that can be reversed by viral-mediated expression of the α5 D398N variant in the medial habenula (MHb). Thus, this study both provides insights into α3β4α5 receptor-mediated mechanisms contributing to nicotine consumption, and identifies the MHb as a critical element in the circuitry controlling nicotine-dependent phenotypes.

The neural cell adhesion molecule (NCAM) promotes axonal outgrowth, presumably through an interaction with the fibroblast growth factor receptor (FGFR). NCAM also has a little-understood ATPase activity. We here demonstrate for the first time a direct interaction between NCAM (fibronectin type III [F3] modules 1 and 2) and FGFR1 (Ig modules 2 and 3) by surface plasmon resonance (SPR) analysis. The structure of the NCAM F3 module 2 was determined by NMR and the module was shown by NMR to interact with the FGFR1 Ig module 3 and ATP. The NCAM sites binding to FGFR and ATP were found to overlap and ATP was shown by SPR to inhibit the NCAM-FGFR binding, indicating that ATP probably regulates the NCAM-FGFR interaction. Furthermore, we demonstrate that the NCAM module was able to induce activation (phosphorylation) of FGFR and to stimulate neurite outgrowth. In contrast, ATP inhibited neurite outgrowth induced by the module.

The nicotinic acetylcholine receptor (nAChR) is the prototype member of the superfamily of pentameric ligand-gated ion channels. ligand-gated ion channel ͉ x-ray crystallography ͉ cys-loop receptor ͉ protein structure ͉ acetylcholine binding protein

The review is mainly devoted to snake venom a-neurotoxins which target different muscle-type and neuronal nicotinic acetylcholine receptors. The primary and spatial structures of other snake venom proteins as well as mammalian proteins of the Ly-6 family, which structurally resemble the`three-finger' snake proteins, are also briefly discussed. The main emphasis is placed on recent data characterizing the a-neurotoxin interactions with nicotinic acetylcholine receptors.Keywords: acetylcholine receptors; binding surfaces; neurotoxins; primary structure; spatial structure; three-finger' proteins.About 30 years ago, a-bungarotoxin and other a-neurotoxins from the venoms of Elapidae and Hydrophidae snakes (Bungarus, Naja and other species) made possible identification and isolation, from electric eels and rays, of the nicotinic acetylcholine receptor (AChR), the first receptor protein subsequently characterized in detail (reviewed in [1±3]). At present, with the molecular biology methods available, the toxins are less important when researchers are interested in finding and sequencing new receptors. However, receptors belonging to the same family or superfamily might have different pharmacological specificities, which is of prime importance for understanding their function under normal conditions and in pathologies. In this respect, it is an ever expanding arsenal of neurotoxins available to researchers that helps distinguish even subtle pharmacological differences in AChRs.Compared with cloning, progress in determining the spatial structure of receptors and ion channels is much slower. On the other hand, X-ray and NMR solution structures have been elucidated for many peptide and protein neurotoxins. In combination with experimental studies on the receptor± neurotoxin interactions, spatial structures of neurotoxins can shed light on the three-dimensional organization of the respective binding sites in receptors. P R I M A R Y S T R U C T U R E O F T H È T H R E E -F I N G E R ' P R O T E I N Sa-Neurotoxins from snake venoms that potently block nicotinic acetylcholine receptors contain 60±75 amino acid residues and are fixed by 4±5 disulfide bridges (Fig. 1). The major difference between the short-type (four disulfides, 60±62 residues) and long-type (five disulfides, 66±75 residues) a-neurotoxins, which have comparable affinity for the Torpedo and muscle-type AChRs, was known to be in the kinetics of association/dissociation with the receptor. However, as found recently, only long-chain neurotoxins block potently a7 homooligomeric neuronal AChRs. It has also been shown that the integrity of the additional disulfide bridge in the central loop II of neurotoxins (Fig. 2) is essential for high-affinity binding to a7 AChR [4]. The removal of the disulfide bond Cys27±Cys31 in k-bungarotoxin (`neuronal bungarotoxin') selective for neuronal AChRs composed of a3 and b2 subunits also brings about a considerable drop in the affinity for the receptor [5].The venoms of different snakes contain small proteins that have a similar si...