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


The Crystal Structure of a Self-Activating G Protein {alpha} Subunit Reveals Its Distinct Mechanism of Signal Initiation

Janice C. Jones1, Jeffrey W. Duffy1, Mischa Machius2,3, Brenda R. S. Temple1,4, Henrik G. Dohlman1,2*, and Alan M. Jones2,5

1 Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA.
2 Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599, USA.
3 Center for Structural Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
4 R. L. Juliano Structural Bioinformatics Core Facility, University of North Carolina, Chapel Hill, NC 27599, USA.
5 Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA.

Abstract: In animals, heterotrimeric guanine nucleotide–binding protein (G protein) signaling is initiated by G protein–coupled receptors (GPCRs), which activate G protein {alpha} subunits; however, the plant Arabidopsis thaliana lacks canonical GPCRs, and its G protein {alpha} subunit (AtGPA1) is self-activating. To investigate how AtGPA1 becomes activated, we determined its crystal structure. AtGPA1 is structurally similar to animal G protein {alpha} subunits, but our crystallographic and biophysical studies revealed that it had distinct properties. Notably, the helical domain of AtGPA1 displayed pronounced intrinsic disorder and a tendency to disengage from the Ras domain of the protein. Domain substitution experiments showed that the helical domain of AtGPA1 was necessary for self-activation and sufficient to confer self-activation to an animal G protein {alpha} subunit. These findings reveal the structural basis for a mechanism for G protein activation in Arabidopsis that is distinct from the well-established mechanism found in animals.

* To whom correspondence should be addressed. E-mail: hdohlman{at}

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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