Identification of a Ca2+/calmodulin-binding domain within the carboxyl-terminus of the angiotensin II (AT(1A)) receptor

To identify regulators of the type 1A angiotensin II receptor (AT(1A)), me investigated the interaction of cellular proteins with a fusion protein con taining the rat AT(1A) receptor carboxyl-terminus. An similar to 20 kDa cyt oplasmic protein interacted with the fusion protein in a Ca2+-dependent man ner and was identified as calmodulin, A control peptide with high affinity for Ca2+/calmodulin and a peptide corresponding to a membrane proximal port ion of the AT(1A), receptor carboxyl-terminus with analogy to known calmodu lin-binding sequences were synthesised and tested for calmodulin-binding. U sing in vitro binding assays combined with gel shift analysis, we demonstra ted the formation of complexes between calmodulin and both peptides, which were Ca2+-dependent and of 1:1 stoichiometry, Affinity gels produced from t hese peptides also purified calmodulin from cell extracts. These results su ggest a novel feedback regulation of the AT(1A) receptor by Ca2+/calmodulin and identify the membrane proximal region of the carboxyl-terminus as a fo cal point for interactions important for AT1A receptor function. (C) 1999 F ederation of European Biochemical Societies.