Ang II binds to AT receptors via various binding sites. The primary binding site is at the extracellular region of the AT receptor where Ang II interacts with residues in the N-terminus of the AT receptor and its first and third extracellular loops. The transmembrane helices also contribute to the binding via the C-terminal carboxyl group that interacts with Lys in the upper part of helix 5 of the receptor; see figure 1 for details.<br />
The ionic bridge formed between Lys and the carboxyl terminal group of the Phe residue of Ang II is most likely stabilized by the Trp residue. In addition, Phe and Asp in transmembrane helix 6 and Lys and Ser in the outer region of transmembrane helix 3 have also been implicated in Ang II binding. This region may possibly participate in the stabilization of the receptor's ratification and in the formation of the intramembrane binding pocket.