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首页> 外文期刊>Biochemistry >Tryptophan Substitutions Reveal the Role of Nicotinic Acetylcholine Receptor alpha-TM3 Domain in Channel Gating;Differences between Torpedo and Muscle-Type AchR
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Tryptophan Substitutions Reveal the Role of Nicotinic Acetylcholine Receptor alpha-TM3 Domain in Channel Gating;Differences between Torpedo and Muscle-Type AchR

机译：色氨酸替代揭示烟碱乙酰胆碱受体α-TM3域在通道门控中的作用;鱼雷和肌肉型AchR之间的差异

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A recent tryptophan scanning of the alpha-TM3 domain of the Torpedo californica AChR demonstrated that this domain can modulate ion-channel gating [Guzman,G.,Santiago,J.,Ricardo,A.,Marti-Arbona,R.,Rojas,L.,Lasalde-Dominicci,J.(2003) Biochemistry 42,12243-12250].Here we extend the study of the alpha-TM3 domain to the muscle-type AChR by examining functional consequences of single tryptophan substitutions at five conserved positions (alphaM282,alphaF284,alphaV285,alphaA284,and alphaI290) homologous to the alpha-TM3 positions that were recently characterized in the Torpedo AChR.Similarly to the Torpedo AChR,mutations alphaM282W and V285W,which are presumed to face the interior of the protein,did not exhibit functional channel activity.Nevertheless,significant expression levels of these mutants were observed at the oocyte surface.In contrast to the Torpedo AChR,in the muscle-type AChR,tryptophan substitution at positions F284,A287,and I290 produces a significant increase in normalized macroscopic response.Single-channel recordings at low ACh concentration revealed that the increase in AChR sensitivity for the F284W,A287W,and I290W is due to an increase in the mean open duration.These results suggest that tryptophan substitution directly affects channel gating,primarily the channel closing rate.Our results suggest that residues facing the interior of the protein (i.e.,alphaM282 and alphaV285) may similary affect channel gating in Torpedo and muscle-type AChR.However,equivalent mutations (i.e.,F284W and I290W) presumably facing the lipid environment display a very different functional response between these two AChR species.
机译：最近对加州鱼雷AChR的alpha-TM3结构域进行的色氨酸扫描表明，该结构域可以调节离子通道门控[Guzman，G.，Santiago，J.，Ricardo，A.，Marti-Arbona，R.，Rojas， L.，Lasalde-Dominicci，J。（2003）Biochemistry 42,12243-12250]。在这里，我们通过检查五个保守位置上单个色氨酸取代的功能后果，将α-TM3结构域的研究扩展到了肌肉型AChR（与最近在Torpedo AChR中表征的alpha-TM3位置同源的alphaM282，alphaF284，alphaV285，alphaA284和alphaI290）。然而，在卵母细胞表面仍观察到这些突变体的显着表达水平。与鱼雷AChR相比，在肌肉型AChR中，色氨酸在F284，A287和I290位置的取代显着增加。标准化macr在低ACh浓度下的单通道记录表明，F284W，A287W和I290W的AChR敏感性增加是由于平均打开持续时间增加所致。这些结果表明色氨酸取代直接影响通道门控，主要是我们的结果表明，面对蛋白质内部的残基（即alphaM282和alphaV285）可能会类似地影响鱼雷和肌肉型AChR中的通道门控。然而，等效的突变（即F284W和I290W）大概面向脂质在这两个AChR物种之间，环境显示出非常不同的功能响应。

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