To date, there is no atomistic structure for the plant G-protein coupled receptor (GPCR). The GCR1 transmembrane protein is a strong analog candidate. To validate this, we used the GPCR Ensemble of Structures in Membrane BiLayer Environment approach (GENSEMBLE) developed at Caltech, to predict the tertiary structure for GCR1. The predicted structure were then attached to the unactivated G-Protein and equilibrated with long MD after inserting in the membrane. We then used DarwinDock to predict the binding site for two known signaling hormones in plants, abscisic acid (ABA) and gibberellin A1 (GA1). These structures were equilibrated with long MD. Our results show important conformational differences between the equilibrated structures of the docking complexes with GCR1+ABA (cyan in image) and GCR1+GA1 (yellow in image). The intracellular (IC) regions of helices 1 and 5 show the largest displacement differences between both systems, approximately 4.5 Å, while the extracellular (EC) regions of helices 6 and 7 had displacements of about 4 and 8 Å respectively. GCR1+ABA is tightly packed around the binding site. We believe that the observed differences in the intracellular region are related to the activation/inactivation of the G protein, and subsequent cellular signaling processes in plants, including dormancy and germination.

Predicted tertiary structure of the plant G-protein coupled receptor (GCR1) coupled with the Galpha Protein, with and without ligands

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ACS Fall 2022

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