Molecular determinants of electrical rectification of single channel conductance in gap junctions formed by connexins 26 and 32.
Molecular determinants of electrical rectification of single channel conductance in gap junctions formed by connexins 26 and 32.
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DOI：
10.1085/jgp.114.3.339
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发表时间：
1999-09
期刊：
影响因子：
--
通讯作者：
Bargiello TA
中科院分区：
文献类型：
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作者：
Oh S;Rubin JB;Bennett MV;Verselis VK;Bargiello TA
由表达连接蛋白32(Cx32)和表达连接蛋白26(Cx26)的细胞配对形成的异型缝隙连接通道的完全开放状态以一种从任何一种同型通道的电流-电压(I-V)关系无法预测的方式进行整流。利用分子遗传学分析，我们证明了位于氨基末端(M1和D2)和第一胞外环(E42)的带电氨基酸是Cx26和Cx32形成的同型和异型通道完全开放状态的电流-电压关系的主要决定因素。观察到的野生型和突变型通道的I-V关系与Chen和Eisenberg(Chen，D.和R.Eisenberg)的电扩散模型得到的I-V关系非常接近。1993年。生物群落。利用从分子分析中推导出的电荷分布模型，求解了一维Poisson-Nernst-Plank方程。Cx32/Cx26异型通道的整改是由于带电残基的数量和位置不对称造成的。该模型需要引入位于沟道表面附近的部分电荷，以近似观察到的Cx32*Cx26E1同型沟道的线性I-V关系。提供这种部分电荷的最佳候选氨基酸是保守的色氨酸残基(W3)。将残基W3的部分电荷和Cx32E41残基的负电荷纳入同型Cx32和异型Cx26/Cx32通道的Poisson-Nernst-Plank模型中的电荷分布中，得到了与观察到的这些通道的I-V关系非常相似的I-V关系。我们进一步证明了某些信道子状态是纠错的。我们认为，与跨结电压(VJ)相关的与这些亚态的门控相关的构象变化包括缩小通道的细胞质进入，从而增加氨基末端电荷的静电效应。在Cx32/Cx26异型通道中观察到的整流是相似的，尽管没有报道的一些整流性电突触那么陡峭。我们认为，类似的静电机制，通过异型通道的开放和亚态导致整流，足以解释陡峭整流电突触的特性。
The fully open state of heterotypic gap junction channels formed by pairing cells expressing connexin 32 (Cx32) with those expressing connexin 26 (Cx26) rectifies in a way that cannot be predicted from the current–voltage (I–V) relation of either homotypic channel. Using a molecular genetic analysis, we demonstrate that charged amino acids positioned in the amino terminus (M1 and D2) and first extracellular loop (E42) are major determinants of the current–voltage relation of the fully open state of homotypic and heterotypic channels formed by Cx26 and Cx32. The observed I–V relations of wild-type and mutant channels were closely approximated by those obtained with the electrodiffusive model of Chen and Eisenberg (Chen, D., and R. Eisenberg. 1993. Biophys. J. 64:1405–1421), which solves the Poisson-Nernst-Plank equations in one dimension using charge distribution models inferred from the molecular analyses. The rectification of the Cx32/Cx26 heterotypic channel results from the asymmetry in the number and position of charged residues. The model required the incorporation of a partial charge located near the channel surface to approximate the linear I–V relation observed for the Cx32*Cx26E1 homotypic channel. The best candidate amino acid providing this partial charge is the conserved tryptophan residue (W3). Incorporation of the partial charge of residue W3 and the negative charge of the Cx32E41 residue into the charge profile used in the Poisson-Nernst-Plank model of homotypic Cx32 and heterotypic Cx26/Cx32 channels resulted in I–V relations that closely resembled the observed I–V relations of these channels. We further demonstrate that some channel substates rectify. We suggest that the conformational changes associated with transjunctional voltage (Vj)-dependent gating to these substates involves a narrowing of the cytoplasmic entry of the channel that increases the electrostatic effect of charges in the amino terminus. The rectification that is observed in the Cx32/Cx26 heterotypic channel is similar although less steep than that reported for some rectifying electrical synapses. We propose that a similar electrostatic mechanism, which results in rectification through the open and substates of heterotypic channels, is sufficient to explain the properties of steeply rectifying electrical synapses.