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Published 28 October 2002. doi:10.1083/jcb.200207060
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© The Rockefeller University Press, 0021-9525/2002/10/349 $5.00
The Journal of Cell Biology, Volume 159, Number 2, 349-360

Article

Identification of amino acid residues lining the pore of a gap junction channel



I.M. Skerrett1, J. Aronowitz1, J.H. Shin1, G. Cymes2, E. Kasperek1, F.L. Cao3 and B.J. Nicholson1

1 Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY 14260
2 Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
3 Department of Genetics, Emory School of Medicine, Atlanta, GA 30322

Address correspondence to B.J. Nicholson, Dept. of Biological Sciences, 615 Cooke Hall, State University of New York at Buffalo, Buffalo, NY 14260-1300. Tel.: (716) 645-3344. Fax: (716) 645-2871. E-mail: bjn{at}acsu.buffalo.edu

Gap junctions represent a ubiquitous and integral part of multicellular organisms, providing the only conduit for direct exchange of nutrients, messengers and ions between neighboring cells. However, at the molecular level we have limited knowledge of their endogenous permeants and selectivity features. By probing the accessibility of systematically substituted cysteine residues to thiol blockers (a technique called SCAM), we have identified the pore-lining residues of a gap junction channel composed of Cx32. Analysis of 45 sites in perfused Xenopus oocyte pairs defined M3 as the major pore-lining helix, with M2 (open state) or M1 (closed state) also contributing to the wider cytoplasmic opening of the channel. Additional mapping of a close association between M3 and M4 allowed the helices of the low resolution map (Unger et al., 1999. Science. 283:1176–1180) to be tentatively assigned to the connexin transmembrane domains. Contrary to previous conceptions of the gap junction channel, the residues lining the pore are largely hydrophobic. This indicates that the selective permeabilities of this unique channel class may result from novel mechanisms, including complex van der Waals interactions of permeants with the pore wall, rather than mechanisms involving fixed charges or chelation chemistry as reported for other ion channels.

Key Words: connexin32; SCAM; pore lining; accessibility; Xenopus oocyte expression


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