Format

Send to

Choose Destination
See comment in PubMed Commons below
J Biol Chem. 2004 Sep 17;279(38):40137-45. Epub 2004 Jul 22.

Perturbing the linker regions of the alpha-subunit of transducin: a new class of constitutively active GTP-binding proteins.

Author information

1
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA.

Abstract

The GDP-GTP exchange activity of the retinal G protein, transducin, is markedly accelerated by the photoreceptor rhodopsin in the first step of visual transduction. The x-ray structures for the alpha subunits of transducin (alpha(T)) and other G proteins suggest that the nucleotide-binding (Ras-like) domain and a large helical domain form a "clam shell" that buries the GDP molecule. Thus, receptor-promoted G protein activation may involve "opening the clam shell" to facilitate GDP dissociation. In this study, we have examined whether perturbing the linker regions connecting the Ras-like and helical domains of Galpha subunits gives rise to a more readily exchangeable state. The sole glycine residues in linkers 1 and 2 were individually changed to proline residues within an alpha(T)/alpha(i1) chimera (designated alpha(T)(*)). Both alpha(T)(*) linker mutants showed significant increases in their basal rates of GDP-GTP exchange when compared either to retinal alpha(T) or recombinant alpha(T)(*). The alpha(T)(*) linker mutants were responsive to aluminum fluoride, which binds to alpha-GDP complexes and induces changes in Switch 2. Although both linker mutants were further activated by light-activated rhodopsin together with the betagamma complex, their activation was not influenced by betagamma alone, arguing against the idea that the betagamma complex helps to pry apart the helical and Ras-like domains of Galpha subunits. Once activated, the alpha(T)(*) linker mutants were able to stimulate the cyclic GMP phosphodiesterase. Overall, these findings highlight a new class of activated Galpha mutants that constitutively exchange GDP for GTP and should prove valuable in studying different G protein-signaling systems.

PMID:
15271992
DOI:
10.1074/jbc.M405420200
[Indexed for MEDLINE]
Free full text
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for HighWire
    Loading ...
    Support Center