Xenbase Image ID: 117584

Figure 9. Proposed model of the extracellular loop regions of a connexin. (A) Based on the observations presented here, E1 and E2 form stacked, antiparallel β sheets connected by three disulfide bonds, although the bond between the 2 and 2′ cysteines is not directly demonstrated here. The model accounts for the periodicity of cysteine movements between loops that rescue coupling, and how movements of the first and third cysteines within a loop could be accommodated by a change in the orientation of the interloop disulfides, or a sliding of the loops with respect to one another. Equivalent loops from the connexins of the apposed hemichannel are hypothesized to interdigitate in front of and behind the stacked loops shown. Conserved residues are indicated based on alignments of all vertebrate connexins. Filled circles indicate hydrophobic character, and open circles indicate hydrophilic character. Half-filled circles indicate that either no consensus of hydrophilic or hydrophobic residues exists at this location, or the conserved residue at that location has an amphipathic character (e.g., Y). Specific residues are only indicated when at least 14 of the 17 aligned sequences were identical at that position. (B) An artist's impression of the β zip model of how the loops of individual connexins could interdigitate to form a β barrel extension of the gap junction channel at the docking interface between hemichannels. Concentric barrels, according to the model shown in A, would be held together by disulfides and are shown extending from the connexin subunits within the membrane into the extracellular space separating the cells. The loops have been shown with an arbitrary tilt to the perpendicular axis of the barrel, consistent with other known β barrel structures. Image published in: Foote CI et al. (1998) Image reproduced on Xenbase with permission of the publisher and the copyright holder. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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