A carboxyl-terminal tail peptide of neutrophil chemotactic receptor disrupts its physical complex with G protein

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Abstract
The binding of G protein to the N-formyl peptide receptor of human neutrophils was investigated with site-specific synthetic peptides. Peptide CT336/332 (322RALTEDSTQTSDTAT336) from the carboxyl-terminal tail region of the receptor competed with the receptor for binding to bovine Gi protein. The peptide competition was assayed by dissociation of a GTP-sensitive, rapidly sedimenting (7S) form of receptor-G protein complex as analyzed by velocity sedimentation on linear sucrose density gradients. An IC50 of 590 μΜ was determined for CT336/332 peptide. A control peptide, with the reverse sequence, rCT 336/332(336 TATDSTQTSDETLAR322)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 CII140/127 (127VLHPVWT QNHRTVS140) and CIII239/227 (227KIHKQGLIKSSRP239) of the receptor, failed to dissociate the reconstituted receptor-G protein complex. Control peptides from the extracellular region EII184/170 (170KTGTVACTFNFSPWT184) and an unrelated sequence matching a portion of neutrophil cytochrome b, CYT306/296 (296KWITKWTHPFKTIE306), were also ineffective. Our results suggest that the cytoplasmic tail of the formyl chemotactic peptide receptor is involved in its coupling to the signal-transducing G protein.

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