Dynamics of G{alpha}i1 interaction with type 5 adenylyl cyclase reveal molecular basis for high sensitivity of Gi-mediated inhibition of cAMP production

Many physiological and pathophysiological processes are regulated by cAMP. Different therapies directly or indirectly influence the cellular concentration of this second messenger. A wide variety of receptors either activates or inhibits adenylyl cyclases in order to induce proper physiological responses. A key event in this signalling system is the direct and dynamic interaction of Gαi1 subunits with adenylyl cyclases. We established a FRET-based assay between G‑protein subunits and type 5 adenylyl cyclase (AC5) and monitored receptor-stimulated interactions between Gαi1 and AC5 in single intact cells with high temporal resolution. We observed that FRET between Gαi1 and AC5 developed at much lower concentration of agonist compared to the overall Gi‑protein activity resulting in a left-shift of the concentration-response curve by about one order of magnitude. Furthermore, Gi1‑protein-mediated attenuation of AC5-dependent increases in cAMP occurred at comparable low concentrations of agonist. Analysing the dynamics we found the dissociation of the Gαi1 subunits and AC5 to occur significantly slower than the G‑protein deactivation and to be insensitive to RGS4 expression. This led us to the conclusion that AC5, by binding active Gαi1, interferes with G‑protein deactivation and reassembly and thereby might sensitise its own regulation.

Source: BJ Cell - July 10, 2013 Category: Biochemistry Authors: M Milde, A Rinne, F Wunder, S Engelhardt, M Bünemann Tags: BJ Signal Source Type: research