A STRUCTURAL MODEL OF THE TETRODOTOXIN AND SAXITOXIN BINDING-SITE OF THE NA+ CHANNEL
A STRUCTURAL MODEL OF THE TETRODOTOXIN AND SAXITOXIN BINDING-SITE OF THE NA+ CHANNEL
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DOI：
10.1016/s0006-3495(94)80746-5
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发表时间：
1994-01-01
影响因子：
3.4
通讯作者：
FOZZARD, HA
中科院分区：
文献类型：
--
作者：
LIPKIND, GM;FOZZARD, HA
生物物理证据表明，天然存在的海洋毒素河豚毒素（TTX）和蛤蚌毒素（STX）的结合位点位于Na+通道离子渗透途径的外口。我们建立了TTX和STX结合袋的分子模型，由电压门控Na+通道的四个S5-S6环的肽段形成的反平行β发夹组成。对于TTX，胍部分与三个羧基形成盐桥，而两个毒素羟基（C9-OH和C10-OH）在重复I和II上与第四个羧基相互作用。这种排列也导致了与苯丙氨酸或酪氨酸残基的芳香环在脑和骨骼的Na+通道异构体中的疏水相互作用，但不与在心脏异构体中发现的半胱氨酸相互作用。与TTX相比，STX通过其第二个胍基与重复IV上的羧基有一个额外的相互作用位点。该模型令人满意地再现了S5-S6区域突变的影响以及各种毒素类似物的亲和力差异。然而，该模型与先前发表的外前庭和Na+通道孔的选择性区域的模型在重要方面有所不同。从由四个β发夹形成的口袋中去除毒素，发现了一个类似漏斗的结构，该结构终止于一个狭窄的区域，适合作为通道选择性过滤器的候选区域。该区域含有两个羧基（Asp（384）和Glu(942)），它们取代了水合Na+离子中的水分子。模拟该区域的突变，产生Ca2+渗透Na+通道，产生三个羧基(Asp（384), Glu（942）和Glu(1714)）靠近的位点。
Biophysical evidence has placed the binding site for the naturally occurring marine toxins tetrodotoxin (TTX) and saxitoxin (STX) in the external mouth of the Na+ channel ion permeation pathway. We developed a molecular model of the binding pocket for TTX and STX, composed of antiparallel beta-hairpins formed from peptide segments of the four S5-S6 loops of the voltage-gated Na+ channel. For TTX the guanidinium moiety formed salt bridges with three carboxyls, while two toxin hydroxyls (C9-OH and C10-OH) interacted with a fourth carboxyl on repeats I and II. This alignment also resulted in a hydrophobic interaction with an aromatic ring of phenylalanine or tyrosine residues for the brainII and skeletal Na+ channel isoforms, but not with the cysteine found in the cardiac isoform. In comparison to TTX, there was an additional interaction site for STX through its second guanidinium group with a carboxyl on repeat IV. This model satisfactorily reproduced the effects of mutations in the S5-S6 regions and the differences in affinity by various toxin analogs. However, this model differed in important ways from previously published models for the outer vestibule and the selectivity region of the Na+ channel pore. Removal of the toxins from the pocket formed by the four beta-hairpins revealed a structure resembling a funnel that terminated in a narrowed region suitable as a candidate for the selectivity filter of the channel. This region contained two carboxyls (Asp(384) and Glu(942)) that substituted for molecules of water from the hydrated Na+ ion. Simulation of mutations in this region that have produced Ca2+ permeation of the Na+ channel created a site with three carboxyls (Asp(384), Glu(942), and Glu(1714)) in proximity.