| |
[摘要]：Coupling of heterotrimeric G proteins to activated G protein-coupled receptors results in nucleotide exchange on the G alpha subunit, which in turn decreases its affinity for both G beta gamma and activated receptors. N-Terminal myristoylation of G alpha subunits aids in membrane localization of inactive G proteins. Despite the presence of the covalently attached myristoyl group, G alpha proteins are highly soluble after GTP binding. This study investigated factors facilitating the solubility of the activated, myristoylated protein. In doing so, we also identified myristoylation-dependent differences in regions of G alpha known to play important roles in interactions with receptors, effectors, and nucleotide binding. Amide hydrogen deuterium exchange and site-directed fluorescence of activated proteins revealed a solvent-protected amino terminus that was enhanced by myristoylation. Furthermore, fluorescence quenching confirmed that the myristoylated amino terminus is in proximity to the Switch H region in the activated protein. Myristoylation also stabilized the interaction between the guanine ring and the base of the alpha 5 helix that contacts the bound nucleotide. The allosteric effects of myristoylation on protein structure, function, and localization indicate that the myristoylated terminus of G alpha(i) functions as a myristoyl switch, with implications for myristoylation in the stabilization of nucleotide binding and in the spatial regulation of G protein signaling. |
|
