The role of the conserved switch II glutamate in guanine nucleotide exchange factor-mediated nucleotide exchange of GTP-binding proteins.

Abstract

Guanine nucleotide exchange factors (GEFs) regulate the activity of small G proteins by catalysing the intrinsically slow exchange of GDP for GTP. The mechanism involves the formation of trimeric G protein-nucleotide-GEF complexes, followed by the release of nucleotide to form stable binary G protein-GEF complexes. A number of structural studies of G protein-GEF complexes have shown large structural changes induced in the nucleotide binding site. Together with a recent structure of a trimeric complex, these studies have suggested not only some common principles but also large differences in detail in the GEF-mediated exchange reaction. Several structures suggested that a glutamic acid residue in switch II, which is part of the DxxGQE motif and highly conserved in Ras-like G proteins, might have a decisive mechanistic role in GEF-mediated nucleotide exchange reactions. Here we show that mutation of the switch II glutamate to Ala severely impairs GEF-catalysed nucleotide exchange in most, but not all, Ras family G proteins, explaining its high sequence conservation. The residue determines the initial approach of GEF to the nucleotide-loaded G protein and does not appreciably affect the formation of a binary nucleotide-free complex. Its major effect thus appears to be the removal of the P-loop lysine from its interaction with the nucleotide.

DOI: 10.1016/j.jmb.2008.03.011

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Cite this paper

@article{Gasper2008TheRO, title={The role of the conserved switch II glutamate in guanine nucleotide exchange factor-mediated nucleotide exchange of GTP-binding proteins.}, author={Raphael Gasper and Christoph Thomas and Mohammad Reza Ahmadian and Alfred Wittinghofer}, journal={Journal of molecular biology}, year={2008}, volume={379 1}, pages={51-63} }