RT Journal Article
SR Electronic
T1 Origin of the Voltage Dependence of G-Protein Regulation of P/Q-type Ca<sup>2+</sup> Channels
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 14176
OP 14188
DO 10.1523/JNEUROSCI.1350-08.2008
VO 28
IS 52
A1 Yun Zhang
A1 Yu-hang Chen
A1 Saroja D. Bangaru
A1 Linling He
A1 Kathryn Abele
A1 Shihori Tanabe
A1 Tohru Kozasa
A1 Jian Yang
YR 2008
UL http://www.jneurosci.org/content/28/52/14176.abstract
AB G-protein (Gβγ)-mediated voltage-dependent inhibition of N- and P/Q-type Ca2+ channels contributes to presynaptic inhibition and short-term synaptic plasticity. The voltage dependence derives from the dissociation of Gβγ from the inhibited channels, but the underlying molecular and biophysical mechanisms remain largely unclear. In this study we investigated the role in this process of Ca2+ channel β subunit (Cavβ) and a rigid α-helical structure between the α-interacting domain (AID), the primary Cavβ docking site on the channel α1 subunit, and the pore-lining IS6 segment. Gβγ inhibition of P/Q-type channels was reconstituted in giant inside-out membrane patches from Xenopus oocytes. Large populations of channels devoid of Cavβ were produced by washing out a mutant Cavβ with a reduced affinity for the AID. These β-less channels were still inhibited by Gβγ, but without any voltage dependence, indicating that Cavβ is indispensable for voltage-dependent Gβγ inhibition. A truncated Cavβ containing only the AID-binding guanylate kinase (GK) domain could fully confer voltage dependence to Gβγ inhibition. Gβγ did not alter inactivation properties, and channels recovered from Gβγ inhibition exhibited the same activation property as un-inhibited channels, indicating that Gβγ does not dislodge Cavβ from the inhibited channel. Furthermore, voltage-dependent Gβγ inhibition was abolished when the rigid α-helix between the AID and IS6 was disrupted by insertion of multiple glycines, which also eliminated Cavβ regulation of channel gating, revealing a pivotal role of this rigid α-helix in both processes. These results suggest that depolarization-triggered movement of IS6, coupled to the subsequent conformational change of the Gβγ-binding pocket through a rigid α-helix induced partly by the Cavβ GK domain, causes the dissociation of Gβγ and is fundamental to voltage-dependent Gβγ inhibition.