Tbe binding of G protein to tbe N-formyl peptide receptor of human neutrophils was investigated with site-specific syntbetic peptides. Peptide CT 3 / 2 6 2 ('2 2 RALTEDST(lfSDTAT"6) from the carboxyl-terminal taU region of the receptor competed witb the receptor for binding to bovine Gi protein. The peptide competition was assayed by dissociation of a GTP-sensitive, rapidly sedimenting (78) form of receptor-G protein compla as analyzed by velocity sedimentation on linear sucrose density

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... a. An IC 50 of 590 I'M was determined for CT~H peptide. A control peptide, with the reverse sequence, rCTUl ( 336 TATDST(lfSDETLAR' 2 2), did not perturb the sedimentation of the reconstituted receptor-G protein complex up to the highest tested concentration, 3 mM. Other peptides tested, corresponding to central portions of the predicted intracellular loop regions CII\r, ( 12 1VLHPVWT Q.NHRTVS~+ 0 ) and cnn~~ (227KIHKQGLIKSSRP239) of tbe receptor, faUed to dissociate the reconstituted receptor-G protein comflex. Control peptides from the atracellular region EII\~0 (170KTGTVACTFNFSPWTIB4) and an unrelated sequence matehing a portion of neutrophU cytochrome b, CYT~rs (29&KVVITKVVTHPFKTIE'o&), were also inefFective. Our results suggest that the cytoplasmic taU of the formyl chemotactic peptide receptor is involved in its coupling to the signal-transducing G protein.