Role of 14-3-3 proteins in the regulation of G-protein signaling

 

T. Obsil1,2

 

1Charles University in Prague, Faculty of Science, Hlavova 8, 12843 Prague, Czech Republic

2Institute of Physiology, Academy of Sciences of the Czech Republic, Videnska 1083, 14220 Prague 4, Czech Republic

obsil@natur.cuni.cz

 

In response to specific agonist signals, G protein-coupled receptors (GPCR) act as guanine nucleotide exchange factors and promote the exchange of GDP for GTP on the Gα subunit of heterotrimeric G proteins. This process is followed by a dissociation of GTP-bound Gα from the Gβγ subunit. Both Gα and Gβγ are thus activated and can propagate downstream signaling via effectors and second messengers [1]. The deactivation of G protein-mediated signaling occurs via the inherent GTPase activity of the Gα subunit, which causes the hydrolysis of GTP to GDP and subsequent assembly of G protein heterotrimer.

Regulator of G protein signaling (RGS) proteins share a highly conserved 125-amino-acid large domain that was first identified by its ability to negatively regulate GPCR signaling [2]. To date, more that 25 proteins containing RGS or RGS Homology domains have been identified. Some RGS proteins consist of little more that the RGS domain (e.g. RGS1, RGS2, RGS4) while others posses long N-terminal or C-terminal extensions (e.g. RGS3, RGS7, RGS9) that usually contain additional protein-protein interaction motifs and domains [3]. RGS proteins function as GTPase-activating proteins (GAPs) for the Gα subunit of heterotrimeric G proteins. They bind specifically to the GTP-bound forms of Gα and significantly stimulate GTP hydrolysis by stabilizing the transition state.

The activity of RGS proteins is tightly regulated through various mechanisms including posttranslational modifications and interactions with other proteins. Several RGS proteins, e.g. RGS3, RGS4 and RGS7, have been found to interact with 14-3-3 proteins. 14-3-3 proteins are a family of acidic regulatory proteins that function as molecular scaffolds by modulating the structure of their binding partners. Results published by several groups suggested that the 14-3-3 protein binding to selected RGS proteins decreases their inhibitory effect on G protein signaling presumably by blocking the interaction between RGS and Gα subunit [4,5].

To elucidate the mechanism of 14-3-3 protein-dependent regulation of RGS function, we performed biophysical characterization of interactions between RGS3 and 14-3-3ζ protein. Our results show that 14-3-3ζ interacts with both phosphorylated motif located within the N-terminal part of RGS3 and C-terminally located RGS domain. Association of RGS3 with 14-3-3ζ induces a significant structural change within the RGS domain, which can explain the observed 14-3-3 protein-dependent inhibition of RGS3 function.

 

References

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4.     T. Benzing, M.B. Yaffe, T. Arnould, L. Sellin, B. Schermer, B. Schilling, R. Schreiber, K. Kunzelmann, G.G. Leparc, E. Kim, G. Walz, J. Biol. Chem., 275, (2000), 28167.

5.     J. Niu, A. Scheschonka, K.M. Druey, A. Davis, E. Reed, V. Kolenko, R. Bodnar, T. Voyno-Yasenetskaya, X. Du, J. Kehrl, N.O. Dulin, Biochem. J., 365, (2002), 677.

 

Acknowledgements.

This work was funded by Grant IAA501110801 of the Grant Agency of the Academy of Sciences of the Czech Republic, by Research Project MSM0021620857 and Centre of Neurosciences LC554 of the Ministry of Education, Youth, and Sports of the Czech Republic, and by Research Project AV0Z50110509 of the Academy of Sciences of the Czech Republic.