Differential Interactions of the C terminus and the Cytoplasmic I-II Loop of Neuronal Ca2+ Channels with G-protein α and βγ Subunits

Abstract

Interactions of G-protein ␣ (G␣) and ␤␥ subunits (G␤␥) with N-(␣ 1B ) and P/Q-type (␣ 1A ) Ca 2؉ channels were investigated using the Xenopus oocyte expression system. G i3 ␣ was found to inhibit both N-and P/Q-type channels by receptor agonists, whereas G␤ 1 ␥ 2 was responsible for prepulse facilitation of N-type channels. L-type channels (␣ 1C ) were not regulated by G␣ or G␤␥. For N-type, prepulse facilitation mediated via G␤␥ was impaired when the cytoplasmic I-II loop (loop 1) was deleted or replaced with the ␣ 1C loop 1. G␣-mediated inhibitions were also impaired by substitution of the ␣ 1C loop 1, but only when the C terminus was deleted. For P/Q-type, by contrast, deletion of the C terminus alone diminished G␣-mediated inhibition. Moreover, a chimera of L-type with the ␣ 1B loop 1 gained G␤␥-dependent facilitation, whereas an L-type chimera with the Nor P/Q-type C terminus gained G␣-mediated inhibition. These findings provide evidence that loop 1 of N-type channels is a regulatory site for G␤␥ and the C termini of P/Q-and N-types for G␣.

Molecular Pathogenesis of Spinocerebellar Ataxia Type 6

“…One functional distinction concerns the ␤4 auxiliary subunit, which selectively binds to the ␣1A C-terminus, and upon binding alters channel kinetics. 33,34 Interestingly, the polyglutamine tract, which is expanded in SCA6, is only present in ␣1A subunits, and is not evolutionarily conserved, as polyglutamine tracts are not present in rodent ␣1A C-termini. A complete understanding of the function of the C-terminus is imperative because the SCA6 mutation is contained within the distal C-terminus of ␣1A, and the therapeutic target will invariably affect C-terminal functioning.…”

G protein inhibition of CaV2 calcium channels

“…85 The C-terminus was identified as being essential for modulation of Ca V 2.3, 113 but other studies suggest it plays more of a modulatory role in Ca V 2.2 channels, perhaps by increasing the affinity of binding and hence responses to low concentrations of free Gβγ. 110,114,115 A variety of other signaling proteins bind to the C-terminus including calmodulin, CaMKII, PKC and Gα subunits. 41,116 This might facilitate crosstalk with other signaling pathways to fine tune Gβγ-mediated inhibition, as suggested for binding of Gαq subunits and perhaps PKC.…”

Identification of R(−)‐isomer of efonidipine as a selective blocker of T‐type Ca2+ channels

“…In the same orientation with respect to cytomegalovirus gene transcription, the 7.0-kb EcoRV/NotI fragment containing the entire coding sequence for a 1G from pBlA1G was ligated with the 4.0-kb SmaI/NotI fragment from pEnon-N1 to yield pEA1G1. Similarly, the 7.0-kb HindIII fragment containing the entire coding sequence for a 1C from pSPCDR (Furukawa et al, 1998) was blunted and ligated with the 5.5-kb SmaI fragment from pCI-neo (Promega, WI, U.S.A.) to yield pCIA1C.…”