IDENTIFICATION OF A CRITICAL ASPARTATE RESIDUE IN TRANSMEMBRANE DOMAIN 3 NECESSARY FOR THE BINDING OF SOMATOSTATIN TO THE SOMATOSTATIN RECEPTOR SSTR2

To determine which residues within the rat somatostatin receptor subtype SSTR2 may be interacting with the lys(9) of somatostatin-14 (S-14), mutant SSTR2 receptors were created by mutating asp(89) or asp(122). [I-125 Tyr(11)]S-14 binding to D89A and D89E mutants suggests that asp(89) is not directly involved in S-14 binding. Binding studies with the charge switch mutants, asp(9)S-14 and D122K, suggest that asp(122) may be interacting with the lys(9) of S-14. [I-125 Tyr(11)]asp(9)S-14 displayed saturable binding to D122K with an affinity comparable to that seen with [I-125 Tyr(11)]S-14 and WT SSTR2. These data suggest that the interaction between lys(9) of S-14 and the TM3 asp(122) of SSTR2 represents one contact site between S-14 and SSTR2. (C) 1995 Academic Press, Inc.