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© The Rockefeller University Press, 0021-9525/1998//1187 $5.00
The Journal of Cell Biology, Volume 140, Number 5, , 1998 1187-1197

Article

The Pattern of Disulfide Linkages in the Extracellular Loop Regions of Connexin 32 Suggests a Model for the Docking Interface of Gap Junctions



Cynthia I. Foote, Lan Zhou, Xing Zhu, and Bruce J. Nicholson

Department of Biological Sciences, State University of New York at Buffalo, Buffalo, New York 14260-1300

Connexins, like true cell adhesion molecules, have extracellular domains that provide strong and specific homophilic, and in some cases, heterophilic interactions between cells. Though the structure of the binding domains of adhesion proteins have been determined, the extracellular domains of connexins, consisting of two loops of ~34–37 amino acids each, are not easily studied in isolation from the rest of the molecule. As an alternative, we used a novel application of site-directed mutagenesis in which four of the six conserved cysteines in the extracellular loops of connexin 32 were moved individually and in all possible pairwise and some quadruple combinations. This mapping allowed us to deduce that all disulfides form between the two loops of a single connexin, with the first cysteine in one loop connected to the third of the other. Furthermore, the periodicity of movements that produced functional channels indicated that these loops are likely to form antiparallel β sheets. A possible model that could explain how these domains from apposed connexins interact to form a complete channel is discussed.

Abbreviations used in this paper: Cx32, connexin 32; E1, extracellular loop 1; E2, extracellular loop 2; TM, transmembrane domain; wt, wild-type.

C.I. Foote's present address is Dept. of Anatomy and Cell Biology, Emory University, 1648 Pierce Dr., Atlanta, GA 30322-3030.

Address all correspondence to Bruce J. Nicholson, Dept. of Biological Sciences, State University of New York at Buffalo, Cooke Hall, Box 601300, Buffalo, NY 14260-1300. Tel.: (716) 645-3344. Fax: (716) 645-3776. E-mail: bjn{at}acsu.buffalo.edu


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