In animals, heterotrimeric guanine nucleotide-binding protein (G protein) signaling is initiated by G protein-coupled receptors (GPCRs), which activate G protein α subunits; however, the plant Arabidopsis thaliana lacks canonical GPCRs, and its G protein α subunit (AtGPA1) is self-activating ...
In animals, heterotrimeric guanine nucleotide-binding protein (G protein) signaling is initiated by G protein-coupled receptors (GPCRs), which activate G protein α subunits; however, the plant Arabidopsis thaliana lacks canonical GPCRs, and its G protein α subunit (AtGPA1) is self-activating. To investigate how AtGPA1 becomes activated, we determined its crystal structure. AtGPA1 is structurally similar to animal G protein α 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 α 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.
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Gtpase Acceleration as the Rate-Limiting Step in Arabidopsis G Protein-Coupled Sugar Signaling. Johnston, C.A., Taylor, J.P., Gao, Y., Kimple, A.J., Grigston, J.C., Chen, J., Siderovski, D.P., Jones, A.M., Willard, F.S. (2007) Proc Natl Acad Sci U S A 104: 17317
Organizational Affiliation:
Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA.
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