Analyzing and modeling the inhibitory effect of phosphatidic acid on the GTP-γ-S binding activity of Goα

G proteins are the molecular switches of G-protein-coupled signal transmembrane transduction, which plays a pivotal role in diverse cellular processes. The guanine nucleotide binding states of G alpha-subunits are considered key factors for their functions. We report here that phosphatidic acid (PA) inhibits the [S-35]-GTP gamma S binding activity of Go alpha. To elucidate this inhibitory effect, biochemical analyses are carried out and a structure-based model is proposed. The experimental results show that PA particularly inhibits the activity of the Goa in a dose-dependent manner, whereas other lipids tested do not. Further analysis on the effects of PA analogs demonstrate that a phosphate head group together with at least one fatty acid chain is necessary for the inhibition. Using a lipid-protein binding assay, it is shown that Goa specifically and directly interacts with PA. In addition to these experimental studies, a 3D structure of Goa is constructed, based on sequence homology greater than 70% to E. coli Gi alpha(1). Molecular docking is performed with PA and PA analogs, and the results are compared and analyzed. Collectively, the results of this investigation provide direct experimental evidence for an inhibitory effect of PA on GTP binding activity of Goa, and also suggest a structural model for the inhibitory mechanism. The lipid-protein model suggests that PA may occupy the channel for exchanging guanine nucleotides, thus leading to the inhibition. These findings reveal a potential new drug target for the diseases caused by genetic G-protein abnormalities.