The renin-angiotensin system is involved in multiple conditions ranging from cardiovascular disorders to cancer. The components of the pathway are targets for disease treatments including ACE inhibitors, renin inhibitors and AT1 blockers. However, very little is understood about the molecular mechanisms by which G-protein coupled receptors (GPCRs) are activated by angiotensin peptides. This study addresses three known receptors of the pathway: AT1, AT2, and MAS. Combining biochemical and amino acid variation data with multiple species sequence alignments, structural models, and docking site predictions allows for visualization of how angiotensin peptides may bind and activate the three receptors. It also addresses conserved and variant mechanisms among receptors. Models of each receptor align with a root mean squared deviation of less than 2.1Å with sequence conservation of 14-30% when comparing to another GPCR (rhodopsin), revealing amino acids required to maintain the seven helixes of the structure. This study reveals that MAS possibly differs in binding to angiotensin peptides, favoring a binding to Ang-(1-7) and not Ang II. Consensus amino acids 512 (Lys) and 621 (His), believed to interact with Phe 8 of Ang II are not conserved in MAS but amino acids (118, 233, 231, 268, 419, 719, and 725) predicted to interact with amino acids 1-7 of either Ang II or Ang-(1-7) are conserved. Analysis of MAS related proteins shown to be activated by Ang peptides reveals possible amino acids (114, 120, 318, 342, 426, 526, 527, and 720) that may contribute to homo or heterodimer formations with other membrane bound proteins, a possible mechanism of activation by the MAS receptor family. Finally a new model of Ang II binding and activation of AT1 and AT2 is proposed that correlates data from site directed mutagenesis and photolabled binding. The initial binding occurs between amino acids 512 and 621of either AT1 or AT2 with Phe 8 of Ang II. Then the Phe of Ang II shifts position via conserved aromatic amino acids to the final photolabled position relative to either AT1 (725) or AT2 (336). Our new model of Ang II-receptor interactions can be verified in future experiments to allow for a clear understanding of angiotensin peptide receptors and their interactions with other molecules.
Transfer of Amino Acids across the Intestine: a New Model Amino Acid
