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J. Biol. Chem., Vol. 277, Issue 48, 46001-46009, November 29, 2002

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Unique Isoform of G-interacting Protein (RGS-GAIP) Selectively Discriminates between Two G_o-mediated Pathways That Inhibit Ca²⁺ Channels^*

Patrizia Tosetti, Timothy Turner, Qiang Lü^§, and Kathleen Dunlap^¶

From the Department of Neuroscience, Tufts University School of Medicine and Molecular Cardiology Research Institute, New England Medical Center, Boston, Massachusetts 02111

Regulators of G-protein signaling (RGS) proteins constitute a large family of GTPase-activating proteins for heterotrimeric G proteins. More than 20 RGS genes have been identified in mammals. One of these, the G-interacting protein (GAIP), preferentially interacts with members of the G_i/G_o subfamily of G proteins in mammalian cells, but its selectivity among members of this subfamily in vitro is limited. Here we report the cloning and functional characterization of a unique cDNA isoform of GAIP, derived from embryonic chicken dorsal root ganglion neurons. Chick GAIP is composed of 199 amino acids, organized into a conserved RGS domain (85% identical to human GAIP), and a unique, short N terminus (only 41% identical, 50% homologous to known mammalian orthologues). Consistent with this unique primary structure, chick GAIP has physiological properties that distinguish it from mammalian GAIPs. We have explored the selectivity of chick GAIP in electrophysiological assays of two G_o-mediated forms of Ca²⁺ channel inhibition produced by -aminobutyric acid in chick dorsal root ganglion neurons, voltage-independent inhibition (mediated by G_o) and voltage-dependent inhibition (mediated by G_o). Dialyzing recombinant chick GAIP in these cells selectively reduced voltage-independent inhibition without affecting voltage-dependent inhibition. Mammalian GAIP, tested under identical conditions in previous studies, demonstrated no selectivity between these two inhibitory processes; thus, our results suggest that the functional specificity of chick GAIP is likely to be determined by its unique N terminus.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AF502147.

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				P. Tosetti, N. Pathak, M. H. Jacob, and K. Dunlap RGS3 mediates a calcium-dependent termination of G protein signaling in sensory neurons PNAS, June 10, 2003; 100(12): 7337 - 7342. [Abstract] [Full Text] [PDF]