Research article

Exploring Allosteric Coupling in the alpha-Subunit of Heterotrimeric G Proteins Using Evolutionary and Ensemble-Based Approaches

Kemal Sayar , Ozlem Ugur , Tong Liu , Vincent J Hilser and Ongun Onaran

BMC Structural Biology 2008, 8:23doi:10.1186/1472-6807-8-23

Published:	2 May 2008

Abstract (provisional)

Background

Allosteric coupling, which can be defined as propagation of a perturbation at one region of the protein molecule (such as ligand binding) to distant sites in the same molecule, constitutes the most general mechanism of regulation of protein function. However, unlike molecular details of ligand binding, structural elements involved in allosteric effects are difficult to diagnose. Here, we used two different approaches that utilize fundamentally different and independent information to identify allosteric linkages in the alpha-subunits of heterotrimeric G proteins, which were evolved to transmit membrane receptor signals by allosteric mechanisms.

Results

We analyzed: 1) correlated mutations in the G protein alpha-subunits family, and 2) cooperativity of the native state ensemble of the Galpha-i1 or transducin. The combination of these approaches not only recovered already-known details such as the switch regions that change conformation upon nucleotide exchange, and those regions that are involved in receptor, effector or G-beta-gamma interactions (indicating that the predictions of the analyses can be viewed with a measure of confidence), but also predicted new sites that are potentially involved in allosteric communication among different regions of the G-alpha protein. A summary of the new sites found in the present analysis, which were not apparent in crystallographic data, are given along with known functional and structural information, and implications of the results are discussed.

Conclusions

A set of residues and/or structural elements that are potentially involved in allosteric communication in G-alpha is presented. This information can be used as a guide to structural, spectroscopic, mutational, and theoretical studies on the allosteric network in G-alpha proteins, which will provide a better understanding of G protein-mediated signal transduction.