Amino acids 356–372 constitute a Gi-activator sequence of the α2-adrenergic receptor and have a Phe substitute in the G protein-activator sequence motif

AbstractThe human α2-adrenergic receptor contains the sequence KASRWRGRQNREKRFTF (amino acids 356–372) at the C-terminal end of its third intracellular loop. This sequence satisfies the structural criteria for G protein-activating sequences [(1992) J. Biol. Chem. 267, 8342–8346] except that the C-terminal sequence is B-B-X-X-Phe instead of B-B-X-B or B-B-X-X-B (B: basic residue, X: non-basic residue). Nevertheless, the synthetic peptide corresponding to this sequence (peptide α2-F) was found to activate Gi and Go strongly with a saturated effect at 1–3 μM. Furthermore, the substitution of the C-terminal Phe of peptide α2-F with Arg, Trp, and Tyr (but not Ala or Asp) did not appreciably affect the Gi-activating potency. It is suggested that the C-terminal basic residue of the B-B-X-X-B motif in Gi-activating sequences can be replaced by an aromatic residue