Identification of Three Subunits of the High Affinity ω-Conotoxin MVIIC-sensitive Ca2+ Channel

doi:10.1074/jbc.271.23.13804

Identification of Three Subunits of the High Affinity ω-Conotoxin MVIIC-sensitive Ca²⁺ Channel*

From the ^§ Howard Hughes Medical Institute, Department of Physiology and Biophysics
^‡ Program in Neuroscience, University of Iowa College of Medicine, Iowa City, Iowa 52242 and
^∥ Neuroimmunology Laboratory, Departments of Immunology and Neurology, Mayo Clinic, Rochester, Minnesota 55905

^‴ An Investigator of the Howard Hughes Medical Institute. To whom correspondence should be addressed:
Howard Hughes Medical Institute, University of Iowa College of Medicine, 400 EMRB, Iowa City, IA 52242.
Tel.: 319-335-7867; Fax: 319-335-6957; E-mail: kevin-campbell{at}uiowa.edu; WWW address: http://www-camlab.physlog.uiowa.edu/home.htm.

Abstract

N-, P- and Q-type voltage-dependent Ca²⁺ channels control neurotransmitter release in the nervous system and are blocked by ω-conotoxin MVIIC. In this study, both a high affinity and a low affinity binding site for ω-conotoxin MVIIC were detected in rabbit brain. The low affinity binding site is shown to be present on the N-type Ca²⁺ channel. Using optimized conditions for specific labeling of the high affinity ω-conotoxin MVIIC receptor and a panel of subunit specific antibodies, the molecular structure of the high affinity receptor was investigated. We demonstrate for the first time that this receptor is composed of at least α_1A, α₂δ, and any one of the four brain β subunits. Such association of different β subunits with α_1A and α₂δ components may produce Ca²⁺ channels with distinct functional properties, such as P- and Q-type.

Footnotes

↵^¶ Supported by American Heart Association-Iowa Affiliate Predoctoral Fellowship.
↵^″ Supported by National Institutes of Health, NCI Grant CA-37343.
↵* 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.
↵¹ The abbreviations used are:

CTX

conotoxin

ω-CgTX GVIA

ω-conotoxin GVIA

ω-CTX MVIIC

ω-conotoxin MVIIC

PCR

polymerase chain reaction

FP

fusion protein

GST

glutathione S-transferase

mAb

monoclonal antibody.
- Received December 6, 1995.
- Revision received February 20, 1996.