TY - JOUR
T1 - Voltage-dependent gating of the C×32*43E1 hemichannel
T2 - Conformational changes at the channel entrances
AU - Kwon, Taekyung
AU - Tang, Qingxiu
AU - Bargiello, Thaddeus A.
PY - 2013/2
Y1 - 2013/2
N2 - 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 Vj- 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 C×32 chimera (C×32*43E1). The results indicate that the intracellular pore entrance narrows from ~15 Å to 10 A with loop-gate but not apparently with Vj-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.
AB - 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 Vj- 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 C×32 chimera (C×32*43E1). The results indicate that the intracellular pore entrance narrows from ~15 Å to 10 A with loop-gate but not apparently with Vj-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.
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U2 - 10.1085/jgp.201210839
DO - 10.1085/jgp.201210839
M3 - Article
C2 - 23319727
AN - SCOPUS:84874742226
SN - 0022-1295
VL - 141
SP - 243
EP - 259
JO - Journal of General Physiology
JF - Journal of General Physiology
IS - 2
ER -