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.

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels and can be divided into two groups: muscle receptors, which are found at the skeletal neuromuscular junction where they mediate neuromuscular transmission, and neuronal receptors, which are found throughout the peripheral and central nervous system where they are involved in fast synaptic transmission. nAChRs are pentameric structures that are made up of combinations of individual subunits. Twelve neuronal nAChR subunits have been described, alpha2-alpha10 and beta2-beta4; these are differentially expressed throughout the nervous system and combine to form nAChRs with a wide range of physiological and pharmacological profiles. The nAChR has been proposed as a model of an allosteric protein in which effects arising from the binding of a ligand to a site on the protein can lead to changes in another part of the molecule. A great deal is known about the structure of the pentameric receptor. The extracellular domain contains binding sites for numerous ligands, which alter receptor behavior through allosteric mechanisms. Functional studies have revealed that nAChRs contribute to the control of resting membrane potential, modulation of synaptic transmission and mediation of fast excitatory transmission. To date, ten genes have been identified in the human genome coding for the nAChRs. nAChRs have been demonstrated to be involved in cognitive processes such as learning and memory and control of movement in normal subjects. Recent data from knockout animals has extended the understanding of nAChR function. Dysfunction of nAChR has been linked to a number of human diseases such as schizophrenia, Alzheimer's and Parkinson's diseases. nAChRs also play a significant role in nicotine addiction, which is a major public health concern. A genetically transmissible epilepsy, ADNFLE, has been associated with specific mutations in the gene coding for the alpha4 or beta2 subunits, which leads to altered receptor properties

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

Mal de Meleda is an autosomal recessive inflammatory and keratotic palmoplantar skin disorder due to mutations in the ARS B gene, encoding for SLURP-1 (secreted mammalian Ly-6/uPAR-related protein 1). SLURP-1 belongs to the Ly-6/uPAR superfamily of receptor and secreted proteins, which participate in signal transduction, immune cell activation or cellular adhesion. The high degree of structural similarity between SLURP-1 and the three fingers motif of snake neurotoxins and Lynx1 suggests that this protein interacts with the neuronal acetylcholine receptors. We found that SLURP-1 potentiates the human alpha 7 nicotinic acetylcholine receptors that are present in keratinocytes. These results identify SLURP-1 as a secreted epidermal neuromodulator which is likely to be essential for both epidermal homeostasis and inhibition of TNF-alpha release by macrophages during wound healing. This explains both the hyperproliferative as well as the inflammatory clinical phenotype of Mal de Meleda.

1 The action of niflumic acid was studied on spontaneous and evoked calcium-activated chloride (IC1(ca)) and potassium (IK(Ca)) currents in rabbit isolated portal vein cells.2 With the nystatin perforated patch technique in potassium-containing solutions at a holding potential of -77 mV (the potassium equilibrium potential), niflumic acid produced a concentrationdependent inhibition of spontaneous transient inward current (STIC, calcium-activated chloride current) amplitude. The concentration to reduce the STIC amplitude by 50% (ICM) was 3.6 x 10-6 M.3 At -77 mV holding potential, niflumic acid converted the STIC decay from a single exponential to 2 exponential components. In niflumic acid the fast component of decay was faster, and the slow component was slower than the control decay time constant. Increasing the concentration of niflumic acid enhanced the decay rate of the fast component and reduced the decay rate of the slow component. 4 The effect of niflumic acid on STIC amplitude was voltage-dependent and at -50 and + 50 mV the IC50 values were 2.3 X 10-6 M and 1.1 X 10-6 M respectively (cf. 3.6 x 10-6 M at -77 mV).5 In K-free solutions at potentials of -50 mV and + 50 mV, niflumic acid did not induce a dual exponential STIC decay but just increased the decay time constant at both potentials in a concentrationdependent manner.6 Niflumic acid, in concentrations up to 5 x 10-5 M, had no effect on spontaneous calcium-activated potassium currents.7 Niflumic acid inhibited noradrenaline-and caffeine-evoked IO(C.) with an ICM of 6.6 x 10-6 M, i.e. was less potent against evoked currents compared to spontaneous currents. In contrast niflumic acid (2 x 10-6 M-5 x 105 M) increased noradrenaline-and caffeine-induced I ). 8 The results are discussed with respect to the mechanism of block of ICl(Ca) by niflumic acid and its suitability as a pharmacological tool for assessing the role of Ic(cp) in physiological mechanisms.