G Protein Activation: A Dynamic Process

Abstract

The Gα subunit of heterotirmeric G Proteins is responsible for regulating intracellular signals through guanine nucleotide binding and release, the catalytic rate limiting step. Recent studies have shown interactions of Gα with Guanine nucleotide Exchange Factors (GEFs), including non-receptor-like GEFs, cause dynamic structural changes which facilitate substrate release. Although receptor-G Protein interactions are well known a lack of understanding of non-receptor-G protein interactions still exists, namely Gα interactions with the non-receptor GEF Ric-8A. A 10-to-100 fold decrease in nucleotide exchange rate for Ric-8A compared to receptors has been shown, which begs the question: What is the cause for the decrease between receptor and non-receptor GEF activity? To answer this, the dynamic and structural interactions of Gα-Ric-8A have been probed by fluorescence anisotropy and single-molecule Forster Resonance Energy Transfer (smFRET). Conformational changes in the ms times-scale of inter and intra-domain states and increase segmental motions of the switch (I-III) regions seem to play a role in substrate release.