Dominic P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
J Gen Physiol. 2013 Feb;141(2):243-59. doi: 10.1085/jgp.201210839. Epub 2013 Jan 14.
Voltage is an important parameter that regulates the open probability of both intercellular channels (gap junctions) and undocked hemichannels formed by members of the connexin gene family. All connexin channels display two distinct voltage-gating processes, termed loop- or slow-gating and V(j)- or fast-gating, which are intrinsic hemichannel properties. Previous studies have established that the loop-gate permeability barrier is formed by a large conformational change that reduces pore diameter in a region of the channel pore located at the border of the first transmembrane domain and first extracellular loop (TM1/E1), the parahelix (residues 42-51). Here, we use cadmium metal bridge formation to measure conformational changes reported by substituted cysteines at loci demarcating the intracellular (E109 and L108) and extracellular (Q56) entrance of hemichannels formed by the Cx32 chimera (Cx32*43E1). The results indicate that the intracellular pore entrance narrows from ∼15 Å to ∼10 Å with loop-gate but not apparently with V(j)-gate closure. The extracellular entrance does not appear to undergo large conformational changes with either voltage-gating process. The results presented here combined with previous studies suggest that the loop-gate permeability is essentially focal, in that conformational changes in the parahelix but not the intracellular entrance are sufficient to prevent ion flux.
电压是调节缝隙连接（间隙连接）和连接子基因家族成员形成的未连接半通道开放概率的重要参数。所有连接子通道都显示出两种不同的电压门控过程，称为环或慢门控和 V(j)-或快速门控，这是内在的半通道特性。先前的研究已经确定，环门控渗透率屏障由一个大的构象变化形成，该构象变化减小了位于通道孔的第一个跨膜域和第一个细胞外环（TM1/E1）、parahelix（残基 42-51）边界处的孔直径。在这里，我们使用镉金属桥形成来测量由位于半通道形成的 Cx32 嵌合体（Cx32*43E1）的细胞内（E109 和 L108）和细胞外（Q56）入口处的取代半胱氨酸报告的构象变化。结果表明，环门控但不是 V(j)-门控关闭时，细胞内孔入口从约 15 Å 变窄至约 10 Å。两种电压门控过程均不会引起细胞外入口的大构象变化。这里呈现的结果与以前的研究相结合表明，环门控渗透率基本上是焦点，即 parahelix 中的构象变化而不是细胞内入口的构象变化足以阻止离子流。
