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J. Biol. Chem., Vol. 281, Issue 34, 24678-24686, August 25, 2006

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-Conotoxin OmIA Is a Potent Ligand for the Acetylcholine-binding Protein as Well as 32 and 7 Nicotinic Acetylcholine Receptors^*

Todd T. Talley, Baldomero M. Olivera, Kyou-Hoon Han^¶, Sean B. Christensen, Cheryl Dowell, Igor Tsigelny, Kwok-Yiu Ho, Palmer Taylor, and J. Michael McIntosh^||1

From the Department of Pharmacology, University of California, La Jolla, California 92093-0636, the Department of Biology, University of Utah, Salt Lake City, Utah 84112, the^¶Molecular Anti-Cancer Research Center, Division of Molecular Therapeutics, Korea Research Institute of Bioscience and Biotechnology, Yusong, P. O. Box 115, Daejon, Korea, and the ^||Department of Psychiatry, University of Utah, Salt Lake City, Utah 84132

The molluskan acetylcholine-binding protein (AChBP) is a homolog of the extracellular binding domain of the pentameric ligand-gated ion channel family. AChBP most closely resembles the -subunit of nicotinic acetylcholine receptors and in particular the homomeric 7 nicotinic receptor. We report the isolation and characterization of an -conotoxin that has the highest known affinity for the Lymnaea AChBP and also potently blocks the 7 nAChR subtype when expressed in Xenopus oocytes. Remarkably, the peptide also has high affinity for the 32 nAChR indicating that -conotoxin OmIA in combination with the AChBP may serve as a model system for understanding the binding determinants of 32 nAChRs. -Conotoxin OmIA was purified from the venom of Conus omaria. It is a 17-amino-acid, two-disulfide bridge peptide. The ligand is the first -conotoxin with higher affinity for the closely related receptor subtypes, 32 versus 62, and selectively blocks these two subtypes when compared with 22, 42, and 11 nAChRs.

Received for publication, March 29, 2006 , and in revised form, June 5, 2006.

^* This work was supported by United States Public Health Service Fellowship NS 043063 (to T. T. T.), the KRIBB Research Initiative Program (to K.-H. H.) and Ministry of Science and Technology of Korea Grant NSM0140233 (to K.-H. H.), National Institutes of Health Grants GM48677 (to B. M. O.), R37-GM18360, UO1-DA019372 (to P. T.), and MH53631 (to J. M. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112-0840. Tel.: 801-585-3622; E-mail: mcintosh.mike{at}gmail.com.

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