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© The Rockefeller University Press, 0021-9525/1999//203 $5.00
The Journal of Cell Biology, Volume 146, Number 1, , 1999 203-218

Original Article

{alpha}-Bungarotoxin Receptors Contain {alpha}7 Subunits in Two Different Disulfide-Bonded Conformations



Sergey Rakhilin, Renaldo C. Drisdel, Daphna Sagher, Daniel S. McGeheea, Yolanda Vallejo, and William N. Green

a Department of Pharmacological and Physiological Sciences, Department of Anesthesia and Critical Care, University of Chicago, Chicago, Illinois 60637
Department of Pharmacological and Physiological Sciences, University of Chicago, 947 East 58th Street, Chicago, IL 60637.(773) 702-3774(773) 702-1763

wgreen{at}midway.uchicago.edu

Neuronal nicotinic {alpha}7 subunits assemble into cell-surface complexes that neither function nor bind {alpha}-bungarotoxin when expressed in tsA201 cells. Functional {alpha}-bungarotoxin receptors are expressed if the membrane-spanning and cytoplasmic domains of the {alpha}7 subunit are replaced by the homologous regions of the serotonin-3 receptor subunit. Bgt-binding surface receptors assembled from chimeric {alpha}7/serotonin-3 subunits contain subunits in two different conformations as shown by differences in redox state and other features of the subunits. In contrast, {alpha}7 subunit complexes in the same cell line contain subunits in a single conformation. The appearance of a second {alpha}7/serotonin-3 subunit conformation coincides with the formation of {alpha}-bungarotoxin–binding sites and intrasubunit disulfide bonding, apparently within the {alpha}7 domain of the {alpha}7/serotonin-3 chimera. In cell lines of neuronal origin that produce functional {alpha}7 receptors, {alpha}7 subunits undergo a conformational change similar to {alpha}7/serotonin-3 subunits. {alpha}7 subunits, thus, can fold and assemble by two different pathways. Subunits in a single conformation assemble into nonfunctional receptors, or subunits expressed in specialized cells undergo additional processing to produce functional, {alpha}-bungarotoxin–binding receptors with two {alpha}7 conformations. Our results suggest that {alpha}7 subunit diversity can be achieved postranslationally and is required for functional homomeric receptors.

Key Words: {alpha}-bungarotoxin • {alpha}7 subunits • nicotinic receptors • protein folding • disulfide bonds

© 1999 The Rockefeller University Press

1.used in this paper: 5HT, 5-hydroxytryptamine (serotonin); ACh, acetylcholine; AChR, acetylcholine receptor; Bgt, {alpha}-bungarotoxin; BgtR, {alpha}-bungarotoxin receptor; HA, hemagglutinin; NEM, N-ethylmaleimide; TMR-Bgt, {alpha}-bungarotoxin tetramethylrhodamine

Sergey Rakhilin's present address is Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY 10021.


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