Plant Gα Structure and Properties

Abstract

G-protein-coupled receptors (GPCRs) are a large family of eukaryotic membrane-spanning proteins that convert signals from the outside of a cell to an appropriate response inside the cell. GPCRs typically associate with a heterotrimeric Gαβγ protein. Activated receptors propagate signals by causing the Gα subunit of the heterotrimer to release GDP and to bind GTP. GTP binding causes a conformational change in the Gα protein that triggers heterotrimer dissociation and downstream signaling. In this way, the guanine nucleotide occupancy of the Gα subunit determines the protein structure and activity. Although most of the G protein paradigm has been established by studying animal G proteins, recent research has revealed diverse roles for G protein signaling in plants. The first part of the chapter (Section “Introduction: Structure-Function Relationships in G Protein Signaling” in Chapter “Plant Gα Structure and Properties”) reviews G protein signaling principles, with an emphasis on the information that has been gleaned from atomic structures. The second part (Section “Comparison of Plant Gα Proteins to Mammalian Gα Proteins” in Chapter, “Plant Gα Structure and Properties”) compares plant Gα proteins to animal Gα proteins with an emphasis on how structure confers function for these proteins. Although plant and animal Gα proteins share less than 40% identity, the key residues that confer G protein function are nearly invariant across all G protein families. The third part (Section “Properties of Plant Gα Proteins” in Chapter “Plant Gα Structure and Properties”) describes the physical properties of plant Gα proteins, including kinetic properties, localization, receptor coupling, and effector activation.