Ayad Wafaa A, Locke Darren, Koreen Irina V, Harris Andrew L
Department of Pharmacology and Physiology, New Jersey Medical School, Newark, NJ 07103, USA.
J Biol Chem. 2006 Jun 16;281(24):16727-39. doi: 10.1074/jbc.M600136200. Epub 2006 Apr 6.
Previous work has shown that channels formed by both connexin (Cx)26 and Cx32 (heteromeric Cx26/Cx32 hemichannels) are selectively permeable to cAMP and cGMP. To further investigate differential connexin channel permeability among second messengers, and the influence of connexin channel composition on the selectivity, the permeability of inositol phosphates with one to four phosphate groups through homomeric Cx26, homomeric Cx32, and heteromeric Cx26/Cx32 channels was examined. Connexin channels were purified from transfected HeLa cells and from rat, mouse, and guinea pig livers, resulting in channels with a broad range of Cx26/Cx32 aggregate ratios. Permeability to inositol phosphates was assessed by flux through reconstituted channels. Surprisingly, myoinositol and all inositol phosphates tested were permeable through homomeric Cx32 and homomeric Cx26 channels. Even more surprising, heteromeric Cx26/Cx32 channels showed striking differences in permeability among inositol phosphates with three or four phosphate groups and among isomers of inositol triphosphate. Thus, heteromeric channels are selectively permeable among inositol phosphates, whereas the corresponding homomeric channels are not. There was no discernible difference in the permeability of channels with similar Cx26/Cx32 ratios purified from native and heterologous sources. The molecular selectivity of heteromeric channels among three inositol triphosphates could not be accounted for by simple connexin isoform stoichiometry distributions and therefore may depend on specific isoform radial arrangements within the hexameric channels. Dynamic regulation of channel composition in vivo may effectively and efficiently modulate intercellular signaling by inositol phosphates.
先前的研究表明，由连接蛋白（Cx）26和Cx32形成的通道（异源Cx26/Cx32半通道）对cAMP和cGMP具有选择性通透性。为了进一步研究第二信使之间连接蛋白通道通透性的差异，以及连接蛋白通道组成对选择性的影响，研究了具有一至四个磷酸基团的肌醇磷酸通过同源Cx26、同源Cx32和异源Cx26/Cx32通道的通透性。连接蛋白通道从转染的HeLa细胞以及大鼠、小鼠和豚鼠肝脏中纯化得到，从而得到具有广泛Cx26/Cx32聚合比例范围的通道。通过重组通道的通量评估对肌醇磷酸的通透性。令人惊讶的是，所测试的肌醇和所有肌醇磷酸均可透过同源Cx32和同源Cx26通道。更令人惊讶的是，异源Cx26/Cx32通道在具有三个或四个磷酸基团的肌醇磷酸之间以及肌醇三磷酸的异构体之间显示出显著的通透性差异。因此，异源通道在肌醇磷酸之间具有选择性通透性，而相应的同源通道则没有。从天然和异源来源纯化的具有相似Cx26/Cx32比例的通道在通透性上没有明显差异。异源通道在三种肌醇三磷酸之间的分子选择性不能通过简单的连接蛋白异构体化学计量分布来解释，因此可能取决于六聚体通道内特定异构体的径向排列。体内通道组成的动态调节可能有效且高效地调节肌醇磷酸介导的细胞间信号传导。
