2 BASIC-AMINO-ACIDS IN THE 2ND INNER LOOP OF THE INTERLEUKIN-8 RECEPTOR ARE ESSENTIAL FOR G-ALPHA-16 COUPLING

The involvement of basic residues of interleukin (IL)-8 receptors in c oupling to the Gi and G16 proteins was investigated by using a series of IL-8 receptor mutants, Substitution of the basic amino acids in the third inner loop of the receptor does not alter the abilities of the receptor mutants to activate recombinant G alpha 16 or phosphoinositid e-specific phospholipase C (PLC) beta 2 expressed in COS-7 cells. Howe ver, an IL-8 receptor mutant with double mutations at residues Lys(158 ) and Arg(159) of the second inner loop loses its abilities to activat e G alpha 16 but retains its ability to activate PLC beta 2. The activ ation of PLC beta 2 by an IL-8 receptor that is sensitive to pertussis toxin has been previously demonstrated to be mediated through G beta gamma. Surprisingly, the IL-8 receptor mutants with substitution of Al a for either residue Lys(158) or Arg(159) can still activate G alpha 1 6, which suggests that either of the two basic residues in the second inner loop of the IL-8 receptor is sufficient for G alpha 16 coupling.