期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：16
页码：6267-6272
DOI：10.1073/pnas.0306804101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：P/Q Ca2+ channel activity is inhibited by G protein-coupled receptor activation. Channel inhibition requires a direct G{beta}{gamma} binding onto the pore-forming subunit, Cav2.1. It is characterized by biophysical changes, including current amplitude reduction, activation kinetic slowing, and an I-V curve shift, which leads to a reluctant mode. Here, we have characterized the contribution of the auxiliary {beta}3-subunit to channel regulation by G proteins. The shift in I-V to a P/Q reluctant mode is exclusively observed in the presence of {beta}3. Along with the observation that G{beta}{gamma} has no effect on the I-V curve of Cav2.1 alone, we propose that the reluctant mode promoted by G{beta}{gamma} corresponds to a state in which the {beta}3-subunit has been displaced from its channel-binding site. We validate this hypothesis with a {beta}3-I-II2.1 loop chimera construct. G{beta}{gamma} binding onto the I-II2.1 loop portion of the chimera releases the {beta}3-binding domain and makes it available for binding onto the I-II loop of Cav1.2, a G protein-insensitive channel. This finding is extended to the full-length Cav2.1 channel by using fluorescence resonance energy transfer. G{beta}{gamma} injection into Xenopus oocytes displaces a Cy3-labeled {beta}3-subunit from a GFP-tagged Cav2.1 channel. We conclude that {beta}-subunit dissociation from the channel complex constitutes a key step in P/Q calcium channel regulation by G proteins that underlies the reluctant state and is an important process for modulating neurotransmission through G protein-coupled receptors.
