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Crystal structure of the G alpha protein AtGPA1 from Arabidopsis thaliana
Structural highlights
FunctionGPA1_ARATH Exhibits a fast rate of basal nucleotide exchange. Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems. Together with GCR1, may regulate the cell cycle via a signaling cascade that uses phosphatidylinositol-specific phospholipase C (PI-PLC) as an effector and inositol 1,4,5-trisphosphate(IP(3)) as a second messenger. Promotes abscisic acid (ABA) responses in guard cells. But, together with GCR1 and GB1, acts as a negative regulator of ABA during seed germination and early seedling development. Involved in the blue light (BL) signaling. Together with GCR1 and ADT3, required for BL-mediated synthesis of phenylpyruvate and subsequently of phenylalanine (Phe), in etiolated seedlings. Modulates root architecture (e.g. lateral root formation). Negatively regulated by RGS1.[1] [2] [3] [4] [5] [6] Publication Abstract from PubMedIn 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. The crystal structure of a self-activating G protein {alpha} subunit reveals its distinct mechanism of signal initiation.,Jones JC, Duffy JW, Machius M, Temple BR, Dohlman HG, Jones AM Sci Signal. 2011 Feb 8;4(159):ra8. PMID:21304159[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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