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Sci. Signal., 8 February 2011
Vol. 4, Issue 159, p. ra8
[DOI: 10.1126/scisignal.2001446]


Editor's Summary

Helical Movement
Signaling by heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (GPCRs) in animals is a well-studied process. Binding of ligand to the GPCR results in a conformational change that activates the G protein by inducing the exchange of guanosine triphosphate (GTP) for guanosine diphosphate (GDP) at the G protein {alpha} subunit. The resulting dissociation of the heterotrimer frees the {alpha} and β{gamma} subunits to interact with effector molecules. Arabidopsis lacks the canonical GPCRs of animal cells, and its G protein {alpha} subunit, AtGPA1, is self-activating, exhibiting spontaneous nucleotide exchange. Jones et al. solved the crystal structure of AtGPA1 and compared it to that of a mammalian G{alpha}i1. This analysis showed that the helical domain region of AtGPA1 was disordered compared to that of G{alpha}i1, and molecular dynamics simulations demonstrated its dynamic motion. Substitution of the G{alpha}i1 helical domain with that of AtGPA1 made the resulting chimeric protein self-activating, demonstrating that the helical domain of AtGPA1 regulates nucleotide exchange and endows the plant {alpha} subunit with a distinct mechanism of activation.

Citation: J. C. Jones, J. W. Duffy, M. Machius, B. R. S. Temple, H. G. Dohlman, A. M. Jones, The Crystal Structure of a Self-Activating G Protein {alpha} Subunit Reveals Its Distinct Mechanism of Signal Initiation. Sci. Signal. 4, ra8 (2011).

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