G-protein activation

Receptor activated heterotrimeric G proteins consist of the Galpha and the tightly associated Gbeta-gamma subunits. When a ligand binds to a G protein-coupled receptor, it stabilises a conformation with an high affinity for the G-protein bound to GDP. GDP is then exchanged for GTP on the Galpha subunit. This exchange triggers the dissociation of the Galpha subunit from the Gbeta-gamma dimer and the receptor. Galpha-GTP and Gbeta-gamma, can then modulate different signalling cascades and effector proteins, while the receptor is able to activate another G protein, resulting in an amplification cascade. The Galpha subunit will eventually hydrolyze the attached GTP to GDP by its inherent enzymatic activity, allowing it to reassociate with Gbeta-gamma and start a new cycle.

受体激活的异源三聚体G蛋白由Galpha亚基与紧密相连的Gbeta-γ亚基组成。当配体与G蛋白偶联受体结合时，它能稳定一种与GDP结合的G蛋白具有高亲和力的构象。随后，GDP在Galpha亚基上被GTP所取代。这一交换过程触发了Galpha亚基从Gbeta-γ二聚体和受体的解离。Galpha-GTP和Gbeta-γ亚基随后可以调节不同的信号级联和效应蛋白，而受体则能够激活另一个G蛋白，从而引发级联放大。最终，Galpha亚基将通过其固有的酶活性水解附着的GTP至GDP，使其能够重新与Gbeta-γ亚基结合并启动新一轮的循环。