Molecular evolution of the Angiotensin II receptors AT1 and AT2: Specificity of the sodium binding site in amniota

In vertebrates, the octopeptide angiotensin II (AngII) is an important in vivo regulator of the cardiovascular system. It acts mainly through two G protein-coupled receptors, AT1 and AT2. To better understand the interplay between these receptors throughout the evolution of the renin-angiotensin system (RAS), we combined a phylogenetic study to electrostatics computations and molecular dynamics (MD) simulations of AT1 and AT2 receptors from different species. The phylogenetic analysis reveals a mirror evolution of AT1 and AT2 that are both split in two clades, separating fish from terrestrian receptors. It also indicates that the unusual allosteric sodium binding site of human AT1 is specific of amniota. Other AT1 and AT2 receptors display a canonical sodium binding site with a serine at position 7.46 (Ballesteros numbering). Electrostatics computations and MD simulations support maintained sodium binding to human AT1 with ingress from the extracellular side. Comparison of the sodium binding modes in AT1 and AT2 from humans and eels indicates that the allosteric control by sodium in both AT1 and AT2 evolved during the transition from an aqueous to a terrestrial environment. The unusual S7.46N mutation in amniota AT1 is mirrored by a L3.36M mutation in amniota AT2. The S7.46N mutation increases the specificity of AT1 for AngII relative to Ang derivatives, whereas the L3.36M mutation might have the opposite effect on AT2. Both mutations should contribute to the split of the renin-angiotensin system into the classical (AngII/AT1) and counter-regulatory (Ang1-7/AT2, Mas) arms in amniota. AUTHOR SUMMARYThe analysis of protein sequences from different species can reveal interesting trends in the structural and functional evolution of a protein family. Here, we analyze the evolution of two G protein-coupled receptors, AT1 and AT2, which bind the angiotensin II peptide and are important regulators of the cardiovascular system. We show that these receptors underwent a mirror evolution and that specific mutations of the sodium binding pocket in both AT1 and AT2 occurred in amniota. We underwent electrostatics computations and molecular dynamics simulations to decipher the details of the sodium binding mode in eel and human receptors, as prototype of fish and amniota receptors. Our results suggest that evolution favored an increased specificity of AT1 and a decreased specificity of AT2 for angiotensin II as compared to its derivatives. In turn, these data suggest that mutations in the sodium binding pocket of G protein-coupled receptors might be an efficient way to gain functional evolution.