CONOTOXINS AND HOMERIC NICOTINIC ACETYLCHOLINE RECEPTORS

烟碱乙酰胆碱受体 (nAChR) 是五聚体配体门控离子通道复合物；在哺乳动物中，ca。 16 个不同的基因编码 nAChR 亚基。 nAChR 基因家族的一个独特分支编码形成同聚 nAChR 的亚基；哺乳动物的 α7 nAChR 亚基就是一个例子。 大多数其他哺乳动物 nAChR 亚基仅在存在不止一种类型的亚基时才形成功能性受体。 我们最近发现了一类芋螺肽，即 alpha4/3 芋螺毒素亚家族，它似乎以同聚 nAChR 亚基为目标。 该项目的总体目标是研究 alpha4/3 芋螺毒素与其同聚 nAChR 靶标之间的相互作用；提出了三项一般性举措。第一个涉及两种密切相关的 α4/3 芋螺毒素：α-芋螺毒素 Iml 和 Imll。这两种药物都可以功能性地抑制 α7 烟碱乙酰胆碱受体，但显然是在不同的位点。 α-芋螺毒素 Imll 似乎通过独特的位点发挥作用，与标准竞争性拮抗剂（例如 α-银环蛇毒素）不同。 一个目标是提供这种新型结合位点的分子定义。第二组实验检查了针对软体动物乙酰胆碱结合蛋白的 α4/3 芋螺毒素，该蛋白是 nAChR 配体结合域的模型。 最近在确定 AChBP 结构方面取得的突破为任何配体门控离子通道的配体结合位点提供了第一张详细图片；长期目标是确定 AChBP 是否可以与结合的 alpha4/3 一起结晶 芋螺毒素。另一个目标是确定软体动物系统中各种 alpha4/3 芋螺毒素的靶标。 最后一组实验目标是检查 α4/3 芋螺毒素对模式生物（如秀丽隐杆线虫）的影响。初步工作表明，α-芋螺毒素 Iml 阻断该生物体中的 nAChR。 在许多无脊椎动物系统中，同聚亚基比异聚亚基包含更多比例的 nAChR 亚基；因此，拟议的α4/3芋螺毒素亚家族研究可能为这些生物体中不同烟碱受体谱的有效神经药理学提供基础。

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.