Ion channels formed by a highly charged peptide.
Ion channels formed by a highly charged peptide.
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由高电荷肽形成的离子通道。
DOI：
10.1021/bi00228a028
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发表时间：
1991
期刊：
影响因子：
2.9
通讯作者：
Stroud,RM
中科院分区：
文献类型：
--
作者：
Ghosh,P;Stroud,RM
Department of Biochemistry and Biophysics，University of加州，San弗朗西斯科，加州94143接收于1990年3月29日;修订的Mandarin pt接收于1991年1月10日摘要：一种肽（MA-/？）与烟碱乙酰胆碱受体（AChR）的一个片段相对应，具有两亲性α-螺旋周期性，在人工磷脂双层中形成离子通道。MA-/？离子通道非常稳定，包括两个离散的传导状态，并经历快速的闪烁型关闭。MA-/？与由与M2序列相同的肽（M2-5）形成的连续电导离子通道形成对比[Oiki，S.，Danho，W.，麦迪逊，五，& Montal，M.等人（1988）Proc. Acad. Sci. USA 85，8703-8707]，AChR的推定跨膜区段。也不是MA-/？Nor M2-5充分模拟天然AChR的电生理学特性。我们认为，肽离子通道至少可以分为三大类：离散电导通道，如MA-/？;离子通道蛋白介导细胞间和细胞区室间电和化学信号的跨膜转导（Hille，1984）。理解这些蛋白质的作用机制的一个问题是鉴定构成离子传导通道的残基。这个问题是针对烟碱乙酰胆碱受体（AChR），a。在脊椎动物神经肌肉接头处发现的离子通道。AChR是一种配体门控的阳离子选择性通道，是由四个同源亚基（a/3ay 5）组成的异五聚体，它们以准对称的方式围绕离子通道排列。这种298-kDa的蛋白质复合物具有2.5 nm宽的细胞外漏斗，推测其含有离子通道的入口（Ross et al.，1977年）。离子通道从该大入口变窄至膜内约0.7 nm的表观直径（Mitra等人，1989年;基斯勒等人，1982年）。离子通道的跨膜部分的衬里最有可能由五个准等效片段形成，每个片段来自AChR的每个亚基，呈五聚体排列。AChR的每个亚基含有四个主要疏水的、推定的α-螺旋跨膜区段M1至M4，以及具有两亲性α-螺旋周期性的序列MA。一级序列分析关注MA作为可能的离子通道形成区段，因为其具有两性螺旋周期性（Finer-Moore & Stroud，1984）（图1a）。然而，最近的实验证据表明，M2区（图lb）更可能是离子通道衬里段的候选者（Noda等人，1983年）。虽然通常是疏水性的，但M2片段具有三至五个丝氨酸或苏氨酸，这取决于亚基，这可能有助于离子通道的亲水中心。M2区的突变（Imoto等人，1988;伦纳德等人，1988）和使用通道阻断剂的光标记研究（Giraudat等，1987; Oberthur等人，1986）已经指出了该区段在离子通道功能中的关键作用。GABAa和甘氨酸受体是配体门控的阴离子选择性离子通道，序列与AChR相似，具有类似于M2的片段，但缺乏MA样受体。
Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143 Received March 29, 1990; Revised Manuscript Received January 10, 1991 abstract: A peptide (MA-/?) correspondingto a segment of the nicotinic acetylcholine receptor (AChR) that has amphipathic a-helical periodicity forms ionchannels in artificial phospholipid bilayers. The MA-/? ion channels are very stable, comprise two discrete conductance states, and undergo rapid, flickering-type closings. The discrete-conductance ion channels formed by MA-/? contrast with the continuous-conductance ion channels formed by a peptide (M2-5) identical in sequence with M2 [Oiki, S., Danho, W., Madison, V., & Montal, M.(1988) Proc. Natl. Acad. Sci. USA 85, 8703-8707], a putative transmembrane segment of the AChR. Neither MA-/? nor M2-5 sufficiently mimics the electrophysiological properties of the native AChR. We suggest that peptide ion channels can be classified into at least three general groups: discrete-conductance channels, such as MA-/?; continuous-conductance channels, such as M2-5; and membrane disruptors, such as those formed by short, amphipathic a-helical peptides.Ion channel proteins mediate the transmembrane transduction of electrical and chemical signalsbetween cells and be-tween cellular compartments (Hille, 1984). A problem in understanding the mechanism of action of these proteins is in identifying the residues that constitute the ion-conducting channel. This problem is addressed for the nicotinic acetylcholine receptor (AChR), a. well-studied ion channel which is found at the vertebrate neuromuscular junction. The AChR, a ligand-gated and cation-selective channel, is a heteropentamer of four homologous subunits (a/3ay5), which are ar-ranged quasi-symmetrically around the ion channel. This 298-kDa protein complex possesses a 2.5-nm-wide, extracel-lular infundibulum, whichpresumably contains the entrance to the ion channel (Ross et al., 1977). The ion channel narrows from this large entrance to an apparent diameter of~ 0.7 nm within the membrane (Mitra et al., 1989; Kistler et al., 1982). The lining of the transmembrane portion of the ion channel is most likely formed by five quasi-equivalent segments, one from each subunit of the AChR, in pentameric arrangement. Each subunit of the AChR contains four primarily hydrophobic, putative a-helical transmembrane segments, Ml through M4, as well as a sequence having amphipathic a-helical periodicity, MA. Primary sequence analysis focused attention on MA as a possible ion channel forming segment because of its amphipathica-helical periodicity (Finer-Moore & Stroud, 1984)(Figure la). However, recent experimental evidence indicatesthat the M2 region (Figure lb) is a more likely candidate for the ion channel lining segment (Noda et al., 1983). Although generally hydrophobic, the M2 segment has three to five serines or threonines, depending on the sub-unit, which could contribute to the hydrophilic center of the ion channel. Mutagenesis of the M2 region (Imoto et al., 1988; Leonard et al., 1988) and photolabeling studies using channel blockers (Giraudat et al., 1987; Oberthur et al., 1986) have indicated a key role for this segment in ion channel function. The GABAa and glycine receptors, which are ligand-gated, anion-selective ion channels and are similar in sequence to the AChR, possess a segment resembling M2 but lack an MA-like