Received for publication November 10, 2004.
Revised December 16, 2004.
Accepted for publication December 17, 2004.

A highly conserved glycine within linker I and the extreme C-terminus of G protein subunits interact cooperatively in switching GPCR-to-effector specificity

Abstract

Numerous studies have attested to the importance of the extreme C-terminus of G protein subunits in determining their selectivity of receptor recognition. We have previously reported that a highly conserved glycine residue within linker I is important for constraining the fidelity of receptor recognition by Gq proteins (Heydorn et al., 2004). Herein, we explored whether both modules (linker I and extreme C-terminus) interact cooperatively in switching GPCR-to-effector specificity and created as models mutant Gq proteins in which glycine was replaced with various amino acids and the C- terminal five Gq residues with the corresponding Gi or Gs sequence. Coupling properties of the mutated Gq proteins were determined following coexpression with a panel of thirteen Gi-and Gs-selective receptors and compared with those of G proteins modified in only one module. G proteins modified in both modules are significantly more efficacious in channelling non-Gq selective receptors to Gq-mediated signalling events as compared with those containing each module alone. Additive effects of both modules were observed even if individual modules lacked an effect on GPCR-to-effector specificity. Dually modified G proteins were also superior in conferring high affinity agonist sites onto a coexpressed GPCR in the absence, but not in the presence of guanine nucleotides. Together, our data suggest that receptor-G protein coupling selectivity involves cooperative interactions between the extreme C- terminus and linker I of G proteins and that distinct determinants of selectivity exist for individual receptors.

Key words: G alpha q, G protein, GPCR, chimeric Galpha protein, promiscuous G protein, signal transduction

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