A Comparative Study of Gamma Subunits of A.Thaliana and O.Sativa

Heterotrimeric G-proteins are composed of α, β and γ subunits that have roles as molecular switches to turn on intracellular trafficking by external stimuli. They are involved in multiple developmental processes ranging from early seedling development, organ shape determination to hormone perception and ion-channel regulation.Although the activation mechanism is well understood in animals, recent studies show that the intrinsic signaling and network mechanism in plants have noticeable differences. Unlike animals, plants lack of the canonical G-protein-coupled receptors, thus G protein α subunit is self-activating. Future studies are expected to reveal more components of the heterotrimeric G-protein signal transduction pathways and to identify the mechanisms by which G-proteins regulate plant phenotypic and developmental plasticity. In the present study, we aimed to investigate the activation mechanism of G proteins in Arabidopsis thaliana and rice (Oryza sativa Indica). Their respective gamma subunits (AGG2) and (RGG2) were heterologously expressed in E.Coli, followed by purification, biochemical and structural characterization. AGG2 has disordered structure, which is stabilized by dimerization in the absence of the natural partner, the gamma subunit, under fully reducing conditions. Small angle X-ray solution scattering and thermal stability data show that the AGG2 dimer has an elongated and flexible structure. Recently RGG2 has also been cloned and expressed in E. coli with the aim of purifying the recombinant protein for biochemical and biophysical characterization. Results on comparative analyses of structural features of AGG2 and RGG2 will be presented and discussed in the context of their respective function(s).∗∗We acknowledge support from Turkish Atomic Agency for SAXS measurements at EMBL Hamburg Outstation, DESY, Germany.