A Reporter Mutation Approach Shows Incorporation of the “Orphan” Subunit β3 into a Functional Nicotinic Receptor*
- From the ‡Department of Pharmacology, University College London, Gower St., London WC1E 6BT, United Kingdom and the§Department of Experimental Molecular Biology, Janssen Research Foundation, Turnhoutseweg 30, B-2340 Beerse, Belgium
Abstract
We have investigated whether the neuronal nicotinic subunit β3 can participate in the assembly of functional recombinant receptors. Although β3 is expressed in several areas of the central nervous system, it does not form functional receptors when expressed heterologously together with an α or another β nicotinic subunit. We inserted into the human β3 subunit a reporter mutation (V273T), which, if incorporated into a functional receptor, would be expected to increase its agonist sensitivity and maximum response to partial agonists. Expressing the mutant β3V273T inXenopus oocytes together with both the α3 and the β4 subunits resulted in the predicted changes in the properties of the resulting nicotinic receptor when compared with those of α3β4 receptors. This indicated that some of the receptors incorporated the mutant β3 subunit, as part of a “triplet” α3β4 β3 receptor. The proportion of triplet receptors was dependent on the ratios of the α3:β4:β3 cRNA injected. We conclude that, like the related α5 subunit, the β3 subunit can form functional receptors only if expressed together with both α and β subunits.
Footnotes
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↵* This work was supported in part by a Medical Research Council grant (to D. C.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵¶ To whom correspondence should be addressed: Dept. of Pharmacology, The School of Pharmacy, 29/39 Brunswick Square, London WC1N 1AX, UK. Tel.: 44-171-753-5887; Fax: 44-171-753 5902; E-mail:sivilo{at}cua.ulsop.ac.uk.
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↵1 The abbreviations used are: ACh, acetylcholine; EC50, the agonist concentration that produces 50% of the maximum response; I max, the maximum response to the agonist; n H, the Hill coefficient; TM2, second transmembrane domain.
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- Received March 16, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
