Allosteric inhibition of adenylyl cyclase type 5 by G-protein: a molecular dynamics study

Adenylyl cyclases (ACs) have a crucial role in many signal transduction pathways, in particular in the intricate control of cyclic AMP (cAMP) generation from adenosine triphosphate (ATP). Using homology models developed from existing structural data and docking experiments, we have carried out all-atom, microsecond-scale molecular dynamics simulations on the AC5 isoform of adenylyl cyclase bound to the inhibitory G-protein subunit Gαi in the presence and in the absence of ATP. The results show that Gαi have significant effects on the structure and flexibility of adenylyl cyclase, as observed earlier for the binding of ATP and Gsα. New data on Gαi bound to the C1 domain of AC5 help to explain how Gαi inhibits enzyme activity and to get insight on its regulation. Simulations also suggest a crucial role of ATP in the regulation of stimulation and inhibition of AC5. Author summary The neurons that compose the human brain are able to respond to multiple inputs from other neurons. The chemical “integration” of these inputs then decides whether a given neuron passes on a signal or not. External chemical messages act on neurons via proteins in their membranes that trigger cascades of reactions within the cell. One key molecule in these signaling cascades is cyclic adenosine monophosphate (cAMP) that is chemically synthesized from adenosine triphosphate (ATP) by the enzyme adenylyl cyclase (AC). We are investigating the mechanisms that control how much cAMP is produced as a function of the signals received by the neuron. In particular, we have studied the inhibition effect of a key protein, termed Gαi, on AC, and we compare it with the stimulator effect of another key protein termed Gsα. Using microsecond molecular simulations, we have been able to show how binding Gαi to AC changes its structure and its dynamics so that its enzymatic activity is quenched and that ATP seems to have a crucial role in the regulation of stimulation and inhibition of AC5.