CONOTOXINS AND HOMERIC NICOTINIC ACETYLCHOLINE RECEPTORS

烟碱型乙酰胆碱受体（nAChRs）是五聚体配体门控离子通道复合物;在哺乳动物中，约为100%。16个不同的基因编码nAChR亚基。 nAChR基因家族的一个独特的分支编码形成同源nAChR的亚基;一个例子是哺乳动物α 7 nAChR亚基。 大多数其他哺乳动物nAChR亚基只有在一种以上的亚基存在时才形成功能性受体。 我们最近发现了一类芋螺肽，α 4/3芋螺毒素亚家族，似乎靶向同源nAChR亚基。 该项目的广泛目标是研究α 4/3芋螺毒素及其同源nAChR靶标之间的相互作用;提出了三项一般性倡议。第一个涉及两种密切相关的α 4/3芋螺毒素，α-芋螺毒素Iml和Imll。这两种药物在功能上都能抑制α 7烟碱乙酰胆碱受体，但显然是在不同的部位。α-芋螺毒素ImII似乎通过独特的位点起作用，该位点不同于标准竞争性拮抗剂（例如α-银环蛇毒素）的位点。 一个目标是提供这种新的结合位点的分子定义。第二组实验检查靶向软体动物乙酰胆碱结合蛋白的α 4/3芋螺毒素，所述蛋白是nAChR配体结合结构域的模型。 最近在确定AChBP结构方面的突破提供了任何配体门控离子通道的配体结合位点的第一个详细图片;长期目标是确定AChBP是否可以与结合的α 4/3结合结晶。 芋螺毒素另一个目标是确定软体动物系统中各种α 4/3芋螺毒素的靶标。 最后一组实验目标是检查α 4/3芋螺毒素在模式生物如C.优雅初步研究表明，α-芋螺毒素Iml阻断了这种生物体中的nAChR。 在许多无脊椎动物系统中，同源亚基包括一个更大的分数比异源亚基的nAChR亚基，因此，拟议的α 4/3芋螺毒素亚家族的研究可能提供了一个有效的神经药理学的基础上，在这些生物体中的lifferent烟碱受体的频谱。

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channel complexes; in mammals, ca. 16 different genes encode nAChR subunits. A distinct branch of the nAChR gene family encodes subunits that form homomeric nAChRs; an example is the mammalian alpha7 nAChR subunit. Most other mammalian nAChR subunits form functional receptors only when more than one type of subunit is present. We recently discovered a class of Conus peptides, the alpha4/3 conotoxin subfamily, that appears to target homomeric nAChR subunits. The broad goal of the project is to investigate interactions between the alpha4/3 conotoxins and their homomeric nAChR targets; there are three general initiatives proposed. The first concerns two closely-related alpha4/3 conotoxins, alpha-conotoxins Iml and Imll. Both of these functionally inhibit the alpha7 nicotinic acetylcholine receptor, but apparently at different sites. Alpha-conotoxin Imll appears to act through a unique site, distinct from that of the standard competitive antagonists (such as alpha-bungarotoxin). One goal is to provide a molecular definition of this novel binding site. A second set of experiments examines the alpha4/3 conotoxins that target molluscan acetylcholine binding proteins, which are models for nAChR ligand binding domains. The recent breakthrough in determining the structure of AChBPs provided the first detailed picture of a ligand binding site for any ligand-gated ion channel; a long-term goal is to determine whether the AChBP can be crystallized with a bound alpha4/3 conotoxin. Another goal is to define the targets of various alpha4/3 conotoxins in molluscan systems. A final set of experimental objectives is to examine the effects of alpha4/3 conotoxins in model organisms such as C. elegans. Preliminary work has shown that alpha-conotoxin Iml blocks an nAChR in this organism. In many invertebrate systems, the homomeric subunits comprise a much greater fraction of nAChR subunits than the heteromeric subunits; the proposed study of the alpha4/3 conotoxin subfamily may therefore provide the basis for an effective neuropharmacology for the spectrum of lifferent nicotinic receptors in these organisms.